Well, first of all, people in general aren't perfect beings.
We often make mistakes, we don't think before we speak, we kill, etcetera... When we think about human nature and how we act, independent of our surrounding influences, we see that it is (or was?) normal for us humans to do certain things. Some of us feel compelled to find a partner, a lover, because it ties in with our need for procreation. Then there are most of us, if not all of us, that lie. It's part of the impulse of self-preservation, in which you feel obliged to protect yourself from harm.
Perchance it's because humans are typically depicted as selfish that we tend to only think of ourselves so that when others listen to what you have to say, they deem it as wrong because your opinion is different from theirs.
Again, we barely know anything of this world. We have tons to discover. We're here exploring outer space when we barely know what's in our oceans! Not only is it simply humanoid to just get things wrong sometimes, but we don't know many things. Remember, theories exist because not everything is certain to us.
