Quite often a person believes they understand something when they don't. In this case, no amount of exhortation to understand the chain of reasoning will help.

Quite often a person believes they understand something when they don't. In this case, no amount of exhortation to understand the chain of reasoning will help. Unfortunately, I think there's a false dichotomy here; you have to understand the problem well enough to write useful tests, and if you don't understand a failure mode, you're probably not going to write anything to test it.