Code that you didn't write is basically just a black box. This is even more true if it is undocumented or written in a way that makes it hard to glean informat

Code that you didn't write is basically just a black box. This is even more true if it is undocumented or written in a way that makes it hard to glean information from the code. There is no way I could feasibly sit down and understand the entire flow of their code (especially when it is very poorly principled to begin with). I can manage without a debugger when I handle the code, or when the abstractions in use provide great error handling... but when it's just a giant pile of somebody else's barely-structured cowboy code? Debugger, please! At the moment I'm working on a massive system composed of about 4 years worth of code (written by someone who will readily confess that they are not a programmer) with no step-through debugger. There's a lot of printf going on and at times it is an extremely painful process.