With me it becomes an obsession, although "musical horniness" I suppose is another way of looking at it.
I know really good players who've been playing many years longer than I have, that simply don't have the patience to work out a lick, etc...if they can't get it in 10 minutes.
Once I get a musical thought in my head or an idea or lick I have to work out or a song I feel compelled to learn, "there's no shifting me".
I've been known to spend literally hours (with little breaks in between) working out chord voicings, and riffs, because I HAD to do it. Anything less and I'd feel I was compromising, and wimping out --but that's just me.
I've also been working on 3 different instrumental songs going on over a year now, (talk about obsession) that I want to be able at some point to record and maybe even perform live.
I've just about mastered 2 of them, but the 3rd will take some more time, because there are techniques I needed to learn and become proficient with, in order to play it. I do this strictly for my own self growth as a musician and, for my own amusement. No one who ever hears these final versions, will have any idea or inclination of just how much pain (in some cases) and sweat went into learning them (nor would they care)--but it's all in the name of making what we're playing appear "effortless" to the viewer/listener. I suspect that the really great players have all gone through similar processes.