negative examples
Shower thought from high school: In writing classes we always study the great works of great authors, in part so we can learn to emulate them. Why don't we study bad writing by bad authors so we can learn how to avoid their mistakes?
(Perhaps we're supposed to do that by reading or getting feedback on our own writing. But this seems less efficient, and also means we won't encounter failures of writing that we don't ourselves commit, which won't prepare us to collaborate on larger writing projects.)
One example that brought this thought back was that sometimes at work we argue about how much we should comment our code, and historically I've been pretty unambiguously pro-comments. Of course, abstractly, I know it's possible to go overboard, that bad comments exist; you're not supposed to, you know:
a += 1; // add 1 to a
But, I thought, nobody would actually write a comment like that! I had to see a few examples to internalize that yes, there are more realistic, less egregious comments that people might put in their code that I would consider bad comments and would argue against. Now I'm just pro "the right amount of comments".
I can state more examples, though they're probably less comprehensible: for example, skilled MMO raiders learn not to make a specific mistake from near misses or from watching others, rather than having to make the mistake themselves. Or, that Confucius quote.
子曰：「三人行，必有我師焉。擇其善者而從之，其不善者而改之。」
A solid example of failure is incredibly valuable. Cherish it.