Summary: in this post you will learn when to take the time to use first principles and the three rules for thinking.   

There are tons of people that claim you need to use first principles for all things. People I follow and greatly respect (Naval Ravikant, Shane Parrish, Julia Galef, Eric Weinstein, Scott Alexander, Peter Thiel, Elon Musk, etc.) regular promote first-principle thinking.

The problem is that you cannot use first principles to determine everything. You don’t have the time to do that. You need to rely on proxies who you believed have figured things out and believe in them (until you eventually figure out that the proxies are wrong, frauds, etc.).

For instance, I have never actually done the full proof that the world is round. I don’t actually know, with 100% certainty, the shape of the earth. I use proxies to help me determine that. It might not be round. There might be a conspiracy. Or we might be living inside a simulation. I’m not 100% sure. But I rely on proxies and make an assumption that the world is round (at least for my purposes).

I don’t know (with certainty) that the moon landing in 1969 was real. Some people believe it was faked. But I use proxies who I respect and therefore adopt the belief that the moon landing was real. I believe this even though I have not taken the 100+ hours to prove it myself.

Therefore, I believe the world is round and also believe the moon landing was real. Am I 100% certain? No. But I live life believing it and know that I will likely never take the time to prove either to myself.

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