The more you realize you're an idiot.
We actually know very little. It's a realization that I'm not quite able to put into words. As you learn more about a topic, you discover surprising and incredible truths and how naive and wrong you previously were. But these new truths that you discover will also likely be disproven or nuanced through later discovery.
It can become exhausting to the point of making you want to throw up your hands and give up on acquiring or caring about knowledge at all.
But we must continue forward, boldly acting on the information we have while constantly seeking new information and remaining open to admit error... in everything.