Expectations

So I got my camera today, and I was stoked! I didn't get to explore too much with it because I had a lot of reading to catch up on due to the freakish amounts of tests I had this week, but Im going exploring this weekend and hope to put my camera to good use.
So today I was watching Grey's after I got back from the gym (my new healthy addiction) and Lizzie said something that struck a cord, she said something along the lines of we shouldn't blame ourselves for everything, and we shouldn't expect anything from other people because when we start to expect things from other people we are just building ourselves up for disappointment. I know everyone has heard this before, but it was the first time it actually held some sort of personal meaning to me.
Why do we expect things from others? Is it because we start to trust and care about the person? If we had no expectations from others we wouldn't depend on others therefore be entirely selfsufficient, but is that even possible? Doesn't everybody crave somesort of human contact at some point or another, even if it is something as simple as a one night stand, we expect that person to not tell anyone if that is what we want, or to tell you if they have some sort of STD prior to sex so that you don't become effected, isn't that the right thing to do? Therefore, it is really even possible to not have any sort of expectations from anyone?
Perhaps this is the brutal part of growing up when you learn who to trust and who to avoid, which isn't as simple as it seems especially if you're someone like me who trusts people very easily. I mean it's not like they are wearing a sign around their neck that says "Don't trust me, I will screw you over." I guess I'm an optamist when it comes to meeting new peopel I like to believe that there are still some good people out there and I refuse to have a negative attitude about our society, no matter how fucked up it is, and no matter how many times I've been cheated by it.
I will go on expecting the best from people, and in some cases I probably am setting myself for disappointment, but you know what the good comes with the bad. We have to learn how do deal with every situation, and every fucked up person we meet in our life, because in some twisted cynic way it is makes us stronger. Maybe I'm just expecting too much or being immature, but I don't think I can handle having a negative attitiude anymore, it's hard to be mad, disappointed, and hateful towards the world, and I'm exhauseted. Besides who said that in order to grow up you must have a "realistic" perpective on things, sometimes reality is over rated, and it's okay to be just a be optimistic and expect the best in people.