Music is a great example. I used to play guitar, I don't now because the time investment needed to get to fulfillment is too heavy. I can pick up a guitar and noodle around with it, but the impetus to take it seriously as a hobby is just no longer there, because of all the perceived friction.

Of course, if I'd taken it seriously as a kid, I wouldn't have that friction and I could count the guitar among my regular hobbies. I don't have that same attitude towards the keyboard, which requires far less finger dexterity and thus practice. I'll probably never pick up a guitar for more than a few minutes ever again, but I can see myself buying a keyboard and stand and going at a piece of music for ten minutes or so every day. (it's a bit of a contrived example, the real reason I don't play my guitars at the moment is because I don't like what it does to my fingers.)

This is what I mean by instant gratification. Everybody draws their line differently, but it's hard to argue that the line doesn't or shouldn't exist. A hobby is what you spend your excess time and money on without expecting a financial return from it. Having an impact is fine, but commerce it isn't, otherwise you call it a side project.