No one builds a building by trial and error.

I've been writing computer programs for over 45 years. I immediately know when I get into a codebase written by trial and error because it's full of pointless puzzles, weird code that takes 50 lines to do something that should take 5, and above everything, fragility and potential bugs everywhere.

You will not find edge cases, security violations or other sources of catastrophe by trial and error. The best way to find them is by understanding the code completely and reasoning about it.