Uncertainty is underrated.
Let me tell you about the worst programmer I ever met. I don't like negativity, but sometimes an example of a bad practice makes the best illustration.
It was my first day on a freelance job, and the team went out to lunch. Sitting around the table, one of the business folks asked the worst programmer how he liked the new open source framework. The lead developer had recently moved their homegrown code to this more formal system.
"Well, it's kind of a security risk," he said. "In our own code, if there's a weakness, no one knows about it. But with this open source stuff the world knows the code we're running."
This statement is so far off base, it's what the physicist Wolfgang Pauli called "not even wrong." Open source software has been proven to be safer, because the whole world is looking at it. Linus Torvalds, the creator of Linux, said, "With enough eyes, all bugs are shallow [easy]".
Part of the reason why is because other programmers can catch mistakes staring you in the face. A few days later, I found a rookie security weakness the worst programmer had left, exposing the entire site to total control. So while he had strong opinions about security, he wasn't actually practicing it.
I have more stories about the worst programmer, but they all have the same thing in common: he was totally uninterested in what he didn't know. In fact, he actively struggled against having to learn anything.
The poet Yeats wrote, "The best lack all conviction, while the worst / Are full of passionate intensity." And the worst programmer was certainly passionate, he would argue at the drop of a hat.
This sounds depressing, unless you hear it as advice. To be the best, lack all conviction.
Certainty and confidence are not the same, they're a balance. I start by assuming I know nothing, eliminate as much uncertainty as possible, until I have confidence that I'm making the right decision.
A paradox: if you're convinced there's no way you can possibly be wrong, you probably are. In order to be right, you need to take into account realistic, legitimate doubt.
I'm never certain – modern physics strongly suggests total certainty is impossible. Doubt is uncomfortable, so you have to get used to it. You have to practice it.
Practice uncertainty.