In any case, I disagree with this saying.
The legal definition of insanity is “mental illness of such a severe nature that a person cannot distinguish fantasy from reality, cannot conduct her/his affairs due to psychosis, or is subject to uncontrollable impulsive behavior.”
A person who practices a craft such as a musical instrument, painting, baking, singing, composition, or writing and expects different results is not insane. This is a person who is hopeful that she or he can eventually create something beautiful and/or beneficial, and again then more beautiful, and over and over even more beautiful through time.
Yes, repetition of harmful habits can be fueled from uncontrollable impulsive behavior. That's not necessarily insanity. It could be OCD, or someone with not much common sense, or someone who has an addiction.
Just an itch... for now.