This was my thought. Perhaps it is *very hard* to accurately appraise one's own trading ability. Just like intelligence. Most people consider themselves to be the smartest person they know - an obvious fallacy from the big picture perspective.
The guy who runs OK Cupid did a survey on users opinion of their intelligence. 60% considered themselves genius! Yes, sixty percent! Now it may be that OK Cupid pretty much only draws from the very tippy top of intelligencia, but the much more likely answer is that people generally cannot asses their own intelligence. When you are a dolt, it's very hard to tell - cuz if you could tell, well then you wouldn't actually be a dolt.
Perhaps the same thing applies to trading ability. It seems very easy to look at past trades and say "But I should have done this and next time I will."
This is why NoDoji and I (and others) stress the importance of keeping records, whether in a journal or a spreadsheet. The numbers don't lie. One can rationalize, of course, but there's only so much records can accomplish with regard to maintaining the tether between fantasy and reality.