Formalizing proofs in Lean is tedious because users must spell out every detail, including seemingly trivial steps, to establish correctness to the computer.

“Formalizing a proof or writing math in this formal language, right, is very kind of tedious. You have to spell out every little detail. Um, even things that are kind of trivial or obvious to mathematicians, you need to kind of convince the computer, uh, the, of their correctness.”