You ultimately have to want the skill. The gp would have noticed his skill gradually waning, not suddenly when it had gone, yet as a kid he didn't care for it.
You're right, I don't know what actual skill I had in mind there (one are you are no longer trained in but still use). I meant to say, even when a kid is wise to the danger of not taking lessons, they don't know what subjects are best for them or how many different ones must be pursued.