I think it helps to define commitment in advance. With my son, it was "if I buy this trumpet, you will have to take lessons and practice for 3 years, whether you like it or not. After 3 years you can decide." 3 years is a long time, but that was an expensive instrument!!

My son wants to take some high-level classes this fall, including a college-level music class. If he commits to the class, there's no backing out. (And no obligation to continue that path after the semester is over)