It makes for a very interesting study in the pathology of "programmer's self-delusion", trying to reconcile this remark ("I'd forgottern that my code was moved to a different drive..."), with the remark you made about 80 minutes earlier: Yes, I added a print statement that verified I'm getting into the correct directory, and yes, the directory has "test.dat" in it.

We all do it -- some more than others, perhaps, but no one is immune. The trick is to remember this fact, to recognize when it strikes, and to work out some ploy to circumvent the personal defect... like "Hmm, if someone else besides me were looking at this, what would they ask/look for/test..."