Practice doesn’t make perfect — practice makes permanent.

I play guitar with my thumbs.

Not just my right thumb — it’s normal to use both the thumb and fingers when you are picking the strings — but my left thumb, too.

On the frets of a guitar, you use the fingers of your non-dominant hand to hold down some of the six strings, at precise positions, to play different notes. To play a chord, a guitarist presses a number of different strings on different frets with one hand, while strumming or picking with the other.

A G chord, in tablature notation, is 3–2–0–0–0–3. You hold down the third fret on the first string, the second fret on the second string, and leave the next three strings open. You also hold the third fret on the last string, to play the highest note (even though it is the furthest from you, and lowest on the guitar).

My left thumb makes an appearance around the neck of my guitar, because I learned chords badly. When I was fourteen and teaching myself how to play, I had a friend who knew more chords than me, and he showed me how to make a C chord.

X — 3–2–0–1–0 was what he showed me, and I asked him, ‘What do you do with the top string?’

‘Don’t play that string,’ he said. ‘It’s not part of the chord.’

As I practiced this new chord, I adjusted my fingers in dozens of micro-movements, to avoid playing the top string. X — 3–2–0–1–0 could be strummed if I held my right thumb on the top string, as I flicked with…