I feel the same way. Each character I create either has a piece of me or an aspect I'd loved to express or at least have.
Since I really don't make OC's for fan art I create the character for stories I'd love to share with others.
Though if one of them landing in a fanfic,(which would be incredible rare since I don't really write fan fics) they'd be more of an outside observer either watching the main canon character do their thing or trying their hardest to get back to their own world; and as a side note I don't ship any of my OC's with canon characters because I don't have an interest in that, plus that fact there's a lot of potential to make an good off the wall story without some much shipping.
Again, not true for me... I use the Enneagram personality typing system. I start writing and once I have a feel for the character I figure out which type they want to be and then develop them more from there, continually doing writing exercises to let them interact with different situations to get the hang of their character and how they behave. I'm a very easygoing, quiet, creative, and peaceful person. I am unobtrusive and can almost get pushed around a little bit because I don't like to cause contention. I'd rather stay home and relax or stay with one close person than go out. But let's take Adrian, for example... He's nothing like me. He's confrontational, opinionated, blunt, sarcastic at others' expense, unafraid (so he likes to think), and a little bit wild. I adore him, but I can't think of anything in me that was transferred to him... Unless something between us happens to be the same which would make sense because you usually have some kind of similarities with almost anyone. Anyway, yeah. We're all different and do things differently, which makes everything more interesting