Bits & pieces of everyone you know
Since you're a writer, you're bound to be asked if you include people you know in your stories. I'm willing to bet that while there may be similarities between your characters and your friends, they aren't exact copies. Or weren't intended to be.
I find that people I know are most likely to turn up in walk-on roles, in my stories. Background extras who need a little something to keep from being cardboard, but don't get much attention. Or sometimes, isolated little habits turn up -- a character will suddenly turn out to have my grandfather's fondness for over-easy eggs. Or when confronted with a shelf of identical objects, the character needs to tidy them up to all face in the same direction.
Overall, the people we know aren't necessarily going to be the best fit for our stories. Unless you lead an unusually interesting life...
After you've written several novels, or a pile of short stories -- because you're in this writing thing for the long haul -- you're probably going to see patterns emerge. In terms of characters, there will be common traits and personality types that turn up. Some of that is because, well, you need characters who are willing and able to get the job done. Some of those common traits are there because of your own character, what you find sympathetic/realistic/interesting, and what your gut's biases are.
Is that a bad thing? On one hand, it's good to push your own envelope. That includes working with characters who challenge you to understand their motivations and priorities. On the other hand, it's hard to carry around someone you don't like in your head all day.
Have you worked with characters very different from yourself? Ones you wouldn't want to be around, if it were real life?