I'll have to check that out. Although my advice will be free :-) But I'm sure that many many other good debuggers have developed the same basic techniques independently. Still, the vast majority of programmers could use some improvement in this area. "Quit thinking and look" is exactly what I mean by "don't assume." People tend to get wrapped up their own view of things and forget that empiricism really wins the day. There is often even fundamental denial, as in "what bug? I haven't seen it." Clearly if someone saw it, unless they were hitting the crack pipe, it's real.

You can't have no assumptions. But half the time I help someone debug something they begin with, "it can't be in this part of the code" which is often unfounded. Now if you PROVE that it isn't, that's a different matter.