I read a good post by one of the authors of the Isabelle theorem prover, that got me thinking. The author, Lawrence Paulson, observed that most math proofs are trivial, but writing them (preferably with a proof assistant) is a worthwhile activity, for reasons similar to safety checklists - “Not every obvious statement is true.” As I have been a bit obsessed with doing formalized mathematics, this got me thinking about why I am excited to spend many hours recently writing formalized proofs in Lean for exercises from Tao’s Real Analysis (along with this recent attempt to write a companion to Riehl’s Category Theory In Context). On a very personal level, I just like math, computers and puzzles, and writing Lean proofs feels like doing all three at once. But I do believe formalization is important beyond nerd-snipping folks like me.