What is first principles?
First principles thinking is breaking a problem down to its most basic, provable truths and rebuilding your reasoning from those — instead of reasoning by analogy ("this is how it's usually done"). It's the difference between copying a recipe and understanding why each ingredient is there.
Why it matters
Most conventional wisdom is a bundle of assumptions nobody has re-checked. Reasoning by analogy inherits every one of those assumptions; reasoning from first principles lets you find the ones that are no longer true — which is where the biggest opportunities and simplest solutions hide.
An example
Batteries were "too expensive" for electric cars — by analogy with historical prices. Broken to first principles: what do the raw materials cost on the commodity market? A fraction of the finished pack price. The gap was process, not physics — so the price could fall, and it did.
How to practice it
Pick a belief you hold about your work and ask "what would have to be true for this?" three layers down, until you hit something you can actually verify. Too Hard Pile's first-principles drills hand you real scenarios and make you melt them down before you see any answer.
Reading about mental models doesn't build the reflex — reps do. Too Hard Pile schedules each drill back with spaced repetition so the model is there when a real decision needs it.