[TheOtherHobbes]

Mental models are good. You should have them.

Don't expect them to be complete. You will not be able to solve any non-trivial problem without discovering edge cases, unexpected complications, and misunderstandings that will only be revealed when you start to code.

I don't understand why anyone would believe that a mental model makes a debugger unnecessary. An accurate mental model won't protect you from certain kinds of implementation bugs, or from sneaky hard-to-spot typos that compile but do the wrong thing - etc.