We are very fond of speaking of ourselves as rational creatures, but I cannot be sure that even I am more rational than rationalized. As methodically and carefully as I approach life, and making the decisions that I make, it is very difficult to be sure that I have arrived at a decision through the rational process, or whether I simply use the rational process to justify the decision I want to make.
Every once in a while I catch myself at it - usually a little late. You rationalize a little bit, then you rationalize a little bit more, and then the data come around and slap you in the face and say Yo, you're wrong! This is why I'm very leery about claiming to know things - careful critical examination of the justification is required to be sure it's not just a pleasant rationalization with a giant hole in the middle.