Every so often I'll hear from some "great" food mind never to crack an egg on an edge because the shell will end up in shards and then in the food. And sometimes just for the fun of it, I'll go against my natural instinct of breaking the shell as I normally do, on the edge of the counter and instead do it on a flat surface. Every time, down the line, I end up fishing out bits of shell. I'm still a firm believer in the "corner" method.
What cooking "rule" do you break?