Our most important source of intelligence is culture. We copy what we see others doing and that make us think that we are smart. It's the equivalent to see a Mathematical proof and think that we could also have done it.
Most of our behaviour is based on instinct. That is why it's so hard to lose weight or study an uninteresting topic.
It took humanity one hundred thousand years to realize that writing symbols allowed for a good communication system. And we did that by copy and error, a kind of evolutive process. Nobody sit down for hours until they invented writing.
So, you see the glass half full, I see it half empty, I guess.
But there is usefulness in seeing the glass half empty. As, it makes us more aware of our lakings and biases.
This opinion, I formed by reading many other opinions adding one more step on the evolution of knowledge (maybe I'm wrong and it's just a dead end thou)