The Rat Race Trap blog has a look at one aspect of the irrational decision-making process humans employ, based on the book Predictably Irrational by Dan Ariely. "Professor Ariely describes some experiments which demonstrated something he calls 'arbitrary coherence.' Basically it means that once you contemplate a decision or actually make a decision, it will heavily influence your subsequent decisions. That's the coherence part. Your brain will try to keep your decisions consistent with previous decisions you have made. I've read about that many times before, but what was surprising in this book was the the 'arbitrary' part. ... [In an experiment] the fact that the students contemplated a decision at a completely arbitrary price, the last two digits of their social security number, very heavily influenced what they were willing to pay for the product. The students denied that the anchor influenced them, but the data shows something totally different. Correlations ranged from 0.33 to 0.52. Those are extremely significant."