Merry Christmas! Today I turn an earlier LW shortform into a full post and discuss "unknown knowns" "obvious" ideas that are actually hard to discuss because they're invisible when you don't have them, and then almost impossible to unsee when you do.

Hopefully this is a fun article for like the twenty people who check LW on Christmas!

__

There are a number of implicit concepts I have in my head that seem so obvious that I don’t even bother verbalizing them. At least, until it's brought to my attention other people don’t share these concepts.

It didn’t feel like a big revelation at the time I learned the concept, just a formalization of something that's extremely obvious. And yet other people don’t have those intuitions, so perhaps this is pretty non-obvious in reality.

Here's a short, non-exhaustive list:

Intermediate Value Theorem
Net Present Value
Differentiable functions are locally linear
Grice's maxims
Theory of Mind

If you have not heard any of these ideas before, I highly recommend you look them up! Most *likely*, they will seem obvious to you. You might already know those concepts by a different name, or they’re already integrated enough into your worldview [...]

---

Outline:

(02:04) The Intermediate Value Theorem

(03:54) Net Present Value

(05:24) Differentiable functions are locally linear

(07:01) Grice's maxims

(08:17) The Pig Hates It

(08:20) Theory of Mind

(09:58) Why this all matters

The original text contained 2 footnotes which were omitted from this narration.

---

First published:
December 25th, 2025

Source:
https://www.lesswrong.com/posts/uqnpbDxnhi9aeQ8Hx/unknown-knowns-five-ideas-you-can-t-unsee

---

Narrated by TYPE III AUDIO.

---

Images from the article:

Snowy village street at night with decorated Christmas trees and lights.

Red star tree topper on decorated Christmas tree with overhead light.

Apple Podcasts and Spotify do not show images in the episode description. Try Pocket Casts, or another podcast app.

“Unknown Knowns: Five Ideas You Can’t Unsee” by Linch

LessWrong (30+ Karma)