Why does humanity seem to think so highly of itself?

So we've learned all there is to know, seen all there is to see in our lofty several thousand years of civilization? Surely other aspects of reality would be known already if they existed, because we are they mighty human race! Nothing gets by us unnoticed! Personally I'm not impressed with anything we've done. There's got to be civilizations out there that make us look like howler monkeys doing tricks for globs of peanut butter.