You're crowding in with your preconceptions already. Everything that happened to you today and everything that happened yesterday and everything that you think will happen tomorrow, all of these things have already started whispering to you, telling you what to think.
Forget about what your second-grade teacher taught you. Forget long division (fourth grade, wasn't it?). Forget those girls in the lunchroom in middle school who wore short skirts, and that day your mother yelled at you for the first time, and even the license plate number of the jerk who cut you off last night. Just forget it all.
And who are you?
It's an answerless question because you haven't forgotten any of it. Not even masters of compartmentalization (very few of whom I know personally) can forget anything completely. Even if we think we've forgotten, we haven't. Our experiences aren't all that make us but they do become part of us. They can be set aside but not forgotten.
This isn't a negative thing and it's not quite positive either. That's just how it is. We can make it negative by harping on about our bad memories, make it positive by thinking about the good ones and building on them for a better future. Or (and this is the most likely option) we can just muddle on in the middle somewhere, not really thinking much about philosophy or life or any of it, really.
And this is what we do.
I guess the middle road works pretty well for most of us; contemplating the way things are and the way they work doesn't necessarily contribute to eternal happiness, and neither does living a life of complete ignorance and absence of thought. So, okay, let's keep on taking that middle road.
But we should think a little bit about just how much our preconceptions influence our lives. It's true, they do sometimes keep us from experiencing new things or making snap decisions or being spontaneous or even living. They also help us out sometimes; we use all the information we have accumulated in our lives to make decisions, and educated decisions at that.
But... it's still a good idea to stop.
As the centuries roll past, more and more prejudices and traditions have built up and been passed down in the form of preconceptions. Every day that passes, stereotypes and what we think of as unshakable truths are ensconced more and more into our minds. That's just how society works. And that's fine. But preconceptions can easily lead to prejudices, which can easily lead to societal conflict, which can all too easily lead to war and all of those other nasty problems we run into rather often... And so it won't hurt you to ask yourself:
Just how much control do your preconceptions have over you?