The 8% Rule: How Billy Strings' Mentor Teaches Practice

The Teacher Behind One of the Greatest Players Alive

For the past three years, Billy Strings has quietly been a student at Sonora Guitar Intensive, working one-on-one with mentor Robb Cappelletto to fill gaps in his playing and push his harmonic vocabulary into new territory. On a recent episode of Playback Sessions, filmed at Carter Vintage Guitars in Nashville, Robb sat down with host Spencer Handley to talk about what that mentorship actually looks like from the inside.

What came out of the conversation was less a set of licks and more a complete philosophy of how to learn an instrument. And the single most quotable idea in it is what we are calling the 8% rule.

"You might have to hear it 30 times at 8% speed before you get it, and that's just what it is. Don't get mad at yourself."

The 8% Rule: Ego Is the Only Thing Stopping You

Most players slow a passage down to 75% and, if they still cannot hear it, conclude that they are not good enough. Robb rejects that framing entirely.

He references a friend who once told him that if you cannot hear something at half speed, you are simply not getting it. Robb's response: that is ridiculous. He has taken passages down to 15% speed, sometimes lower, worked them out, and now hears them at full tempo without effort.

"There is a tempo at which you can play anything, and there is a tempo at which you can hear anything. You need to find that tempo and start from that."

The obstacle is almost never ability. It is ego. Slowing a recording to 8% feels like an admission of defeat, so players stay at 60% where their pride is intact and their ears learn nothing. Robb reframes the whole thing with a line worth writing on your case:

"You can or you can't do it. The answer is can't. You do or don't want to. The answer is do."

Practical takeaway: The next time a phrase will not reveal itself, do not nudge the speed from 70% to 65%. Drop it off a cliff. Go to 20%, then 10%, then 8% if you need to. Loop two beats. Hear it, sing it, then find it.

Two Practice Tempos: No Tempo and Near Full Tempo

Here is where Robb gets genuinely contrarian, and where a lot of players are going to have to rethink years of habit.

The standard advice is to play something perfectly slow, then raise the metronome one or two BPM at a time until you arrive at speed. Robb calls this the single biggest misconception in guitar practice, and Andy Wood has said similar things.

"You don't know if the answer is right until you've tried it at tempo."

The problem with the metronome ladder is that a bad fingering or a broken picking pattern can survive at slow tempos indefinitely. You can spend three months creeping upward before you hit a wall that was baked in on day one. The fingering was never going to make it.

So Robb works with two tempos:

• No tempo. Free time, no click. You are checking that the fingering feels comfortable, the picking pattern flows, the string crossings are clean, and nothing in your right hand breaks.
• Near full tempo. Roughly 75% to 85%, fast enough that the mechanics get stress tested. It will not be clean. That is fine. What matters is that no part of it is impossible.

Then you go back and forth. Listen at full speed. Guess the notes. Try it at 80%. Discover that bar three collapses. Pull out the microscope: you are using the middle finger where the ring finger belongs, or you snuck in two upstrokes. Fix it in no tempo. Try it fast again.

"When we finally got the fingering solidified because we can do it at 75 or 85 and it's not clean, but none of it doesn't work, okay, this is the right answer that we're going to refine."

Notice that the 8% rule and the near-full-tempo rule are not in conflict. The 8% is for your ears, for figuring out what the notes actually are. The near-full tempo is for your hands, for validating that your chosen fingering can survive. Two different jobs, two different speeds.

Warming Up Is Not Scales

Robb's morning routine is worth stealing wholesale. Before his computer turns on, before he answers a single message, he plays. A metronome clicks once every four bars, just enough to catch him if his time drifts, not enough to carry him.

He plays through Bach repertoire he has transcribed, or lately a stack of fiddle tunes, Doc Watson and Tony Rice material, so he has more common ground to explore with Billy. Each piece two or three times. The first pass is okay. The second is better. The third is better still.

His definition of a warm-up comes from violinist Hilary Hahn:

"Scales are not a warm-up, because if you want to perform a scale properly, you should be warmed up. A warm-up is something you know you can play on a good day, and you play it until you stop making mistakes."

That is the test. Not a set number of minutes. You are warmed up when the mistakes stop on material you already own.

Robb is candid that as a working professional, the rest of his practice is dictated by what he has to play on Thursday. The Bach and the Doc Watson are his time away from that, his "me time." There is something reassuring in that for anyone who feels their practice has become all obligation.

The Spiral: Why You Should Stop Trying to Review Everything

Students constantly ask Robb how they are supposed to review everything they have learned when they only have an hour a day. His answer is blunt: you do not review. That is his job.

A long-term student described Robb's teaching as a spiral, and the image stuck. Theory, technique, ear training, improvisation, voice leading, you cover all of it at level one, then all of it again at level two, then level three, each pass wider and more complex, each pass quietly rebuilding what came before.

"Don't worry about that. That's going to be built into the next thing that we do."

The goal is what Robb calls the ear-to-fingertip connection. In a real playing situation you cannot think, "this chord is C sharp minor and I want the minor third." The band is already four bars down the road.

Sound First, Theory Second

Robb admits theory never came easily to him, which may be exactly why he has such a clear position on it. He also dismantles the self-taught myth in a single sentence: everybody and nobody is self-taught, because even with the best teacher in the world you are doing 80 to 90% of the work alone, and even with no teacher you got that lick off the internet or from a friend or from watching someone on stage.

On theory itself, the order of operations is everything:

"Theory as an instigator for a sound can often lead to stale or boring or predictable players."

Robb never opens with "play an arpeggio off the third of that chord." He starts with a solo. You learn it, you sing it, you play it. Then he points out that the thing you already love in bar three is an arpeggio built off the third. Now theory becomes what it is genuinely good for: consistency, understanding, and portability. You know that sound in D, now take it to E, G, and D flat.

He argues you need three redundant ways of knowing any piece of music: by sound, by theory and note name, and by shape or feel under the fingers. In performance, one or two of those will fail you. If you cannot recall whether it was ring finger or pinky, the note name saves you. It is E. Go.

He is similarly skeptical of buzzword chasing. If you heard triad pairs or negative harmony on a record and fell in love with the sound, wonderful. If you are exploring a concept with no sound in mind, go listen to some records.

Put the Tabs Away

This is the takeaway most players will resist.

"If you need the tabs, the tabs won't get you all the way there."

Robb spent a summer sight-reading the Bach Chaconne every morning like reading the newspaper. He cannot play a note of it today. The violin sonatas he learned by ear, like a Coltrane solo at 18% speed, are memorized so deeply he can play them anywhere, anytime.

When he does use written material, the process is fixed, borrowed from a teacher he studied with only once or twice in high school: read the chart once, turn it over, try to play it. When you get stuck, genuinely try to remember first. Only then flip the page for the answer, and flip it back immediately. You are training memory, not reading.

He gives most students videos instead of tabs, and his reasoning is sharp: the iPhone has rendered sheet music largely pointless for capturing ideas. A video lets you hear the notes and see the frets, which on guitar matters more than it does on piano. A video is not spoon-feeding, because it shows you what the sound looks like the way you will actually be seeing it.

Time Is the Most Important Thing

Asked what he wishes every student knew, Robb did not hesitate. Time. On every instrument.

A drummer can master every rudiment and it is all wasted if the pulse wanders. A guitarist can build enormous technique, but if the phrasing does not sit on the beat, none of it lands. Yet education overwhelmingly focuses on notes, notes, theory, notes.

He has heard teachers claim rhythm cannot be taught, and calls that the biggest load of crap he has heard. His approach depends on the player. Some students simply need to count what they cannot yet hear. Some need a click and the simplest possible right-hand motion to build a foundation on. And some are already technically accurate but stylistically flat.

"You played the right rhythm, but David Gilmour is more laid back than you."

Sitting behind the beat, pushing ahead of it, swinging a certain way, these are all trainable. And in every single case, the method is the same: slow it down until you can hear the difference.

Nobody Was a Magician

The thread running through all of this is Robb's refusal to accept "because I said so" as an answer, either from his old teachers or from himself. He shared a story about a student, a doctor, who sent him an article on how the word instinct gets used in the sciences. Instinct, the article argued, is the term we reach for when we have decided not to look any further.

"All of our heroes, none of them were magicians. If you really love Pat Metheny but there's just something he's doing that you're not, look closer. You can find the answer. It doesn't mean it's going to be easy. It doesn't mean it's going to be simple, but the answer is there if we look."

Your Practice Checklist

• Warm up on material you already own, not scales, and stop when the mistakes stop.
• Use one metronome click every four bars to expose your time rather than prop it up.
• When transcribing, go as slow as you need to. 15%, 10%, 8%. Ego is the obstacle, not ability.
• Stop climbing the metronome one BPM at a time. Work in no tempo and near full tempo, and bounce between them.
• Test fingerings at 75 to 85% early so you find the ones that will never make it.
• Learn the sound first, name it with theory second.
• Get off the page as fast as possible. Read once, flip it over, try to remember.
• Prioritize time and tone above note choice.

Find the Gaps in Your Own Playing

Billy Strings came into his first lesson already able to play better than most players ever will, and he still filled out an intake form listing the gaps he wanted to close. That humility is the whole story. If you have been playing for years and you can feel yourself plateauing without being able to name why, the Sonora Guitar Skills Assessment is a free one-on-one with a Sonora coach. In about 50 minutes you get an 18-point diagnostic of your playing, a written report naming the two or three things actually holding you back, and a 30-day practice plan.