I don't think this was intended to be an either/or choice, and "quit thinking and look" can be read as "if thinking isn't working, get more data" (and it could

I don't think this was intended to be an either/or choice, and "quit thinking and look" can be read as "if thinking isn't working, get more data" (and it could be read as such even if that wasn't the author's intended meaning!) Even if thinking has not solved the problem, it may help you find where to look next. One tip I have is that even if you wrote the code and think you know how it works, stepping through it in your mind might lead you to see where you are making a questionable assumption. You may think that you can do that just as well in the debugger, and you may be right, but there are two ways of using the debugger: one is to hit 'step' and see what happens; the other is to figure out what you expect will happen, and then check if your expectation was correct. There have been many times when I have stepped up to the point where the bug is about to happen, and then realized what is wrong before taking that final step.