Edge cases are good reasons. In some cases a single edge case can be the reason to make a decision. If your attitude is “working in 99% of cases is good enoug

Edge cases are good reasons. In some cases a single edge case can be the reason to make a decision. If your attitude is “working in 99% of cases is good enough”, that means over a long enough period of use, 100% of your users will encounter an edge failure. The way to even have a shot at 99% of your users a good experience is to constantly let edge cases force your hand.