I used to be a one project gal ... that seems to have fallen by the wayside and and also seems to have happened without me noticing!
I now do not seem to be happy unless I have multiple projects on the go and have one for various different situations that I may find myself in; purse knitting, TV/podcast knitting, something to challenge or a new technique I want to try and of course the ever growing list of knitting for hire / gift knitting.
I love knitting for other people .. for years my knitting was secret, and I don't mean the secret projects here and there, I mean completely secret, for reasons I will not go into here, I hid my knitting away from public view .. thankfully I saw the error of my ways and have been encouraged by almost everyone since and when I am therefore asked to knit something specific by someone I see that as compliment that first they believe I will be able to complete the said project and also that they feel they know me well enough to ask me. I knit all the time anyway and so I do not see it as an inconvenience to knit for others and if they are also paying for the materials (even if not my time) then that's a bonus as it actually saves me spending money on stash enhancement...!
I knit for the pure enjoyment of it and the pleasure is magnified if someone else appreciates it, I only have one friend who has specifically asked me not to knit her anything .... I don't see her very much anymore :)