I usually think of it as a very scientific inspired process. Information gathering - Hypothesis forming - testing - evaluation. Easy problems / bugs require ne

I usually think of it as a very scientific inspired process. Information gathering - Hypothesis forming - testing - evaluation. Easy problems / bugs require next to no hypothesis. You just see the error, backtrace or whatever and can go fix it. But harder bugs and system bugs usually require information gathering and analysis of that information to figure out and form a good hypothesis. To do that, just like your mentor said, you need good knowledge of the code and good understanding of what the information is telling you and what that can suggest or rule out.