100 authors spent decades writing a proof so long that nobody has ever read the whole thing. 15,000 pages, 500 papers. Turns out one piece of it had a flaw the entire time, and a lot of the people who could have caught it are in their eighties now. The theorem is called the Classification of Finite Simple Groups, basically the periodic table for symmetry. Physicists lean on it for work on black holes. Mathematicians cite it constantly without anyone having checked all of it, since doing that…