About 400 years ago, the French mathematician Pierre de Fermat left the world a famous riddle, which we now call Fermat's Last Theorem. It took us until 1994 to prove it, by Andrew Wiles, and another year to reprove it, by the same person, after a small mistake was detected by a peer. Which is curious: if mathematics is praised for its objectivity, can two people have two different interpretations? If for Wiles the theorem was proven, in an objective field, we should suspect that the same conclusion could be reached by everyone else. What made him think the proof was finished? Who decides where to stop?