I would argue that it's impossible to distinguish what is "you." From the time you're born, you take in information and form beliefs, and some of your most influential sources of information are your parents, then siblings, then friends, at different stages of your life. All of this contributes to your own preferences and ways of engaging with the world. In other words, other people have a huge part in shaping your personality.

Genes and environment play a pretty big role as well. I saw a study that showed that people who read a lot tend to take on characteristics of the main characters.

I guess what I'm trying to say is we're all just meat machines, taking in input, integrating it, and spitting out outputs. There is this overwhelming sense of "self" and "identity," but when you try and pin down what those things entail, it's this infinitely small thing.