Russell's Paradox & the Foundations Crisis
Bertrand Russell · 1901
"Russell showed that naive set theory lets you define 'the set of all sets that don't contain themselves,' which both contains and doesn't contain itself — forcing mathematics to rebuild its foundations with stricter rules."
Gottlob Frege thought he had finished the foundations of mathematics. Russell found the counterexample in 1901 and mailed it to him in June 1902, as Frege's second volume was going to press: 'the set of all sets that do not contain themselves' — and Frege's system collapsed.
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The Law of Large Numbers
"As you take more independent draws from the same process, the average of what you see converges to the true underlying expectation — which is why small samples routinely mislead and large samples quietly correct."