"Man's real treasure is the treasure of his mistakes, piled up stone by stone through thousands of years," writes the great Spanish philosopher Jose Ortega y Gasset in his 1941 book, Toward a Philosophy of History. Though we flatter ourselves by always "wanting to begin again," civilization requires that we never break our continuity with the past, for it is the very memory of what has gone grievously wrong that is the signal requirement for progress.
Not to fail, not to be wrong, is inhuman. And there are no more callow, uninteresting personalities than those who claim or feel themselves to have always been right and who have never known humiliation. Failure and being wrong are things that we should hold dear, as prized possessions, and learn from constantly; they are more valuable than money in the bank or degrees from elite schools. The young are seen to be unwise and shallow not because they are made that way, but because they haven't accumulated enough years yet to make the kind of humiliating mistakes and to suffer the hardships that are a precondition for the true enrichment of character.
Without the career mistakes made by Thucydides and Machiavelli, we might never have had The Peloponnesian War and The Prince, arguably the two greatest, seminal works of international relations.