I tend to dislike posting links to blogs, but this one seemed very appropriate for this sub-forum: http://badanalysis.blogspot.com/2006/10/10-reasons-your-co-workers-make-stupid.html It discusses some of the reasons people make bad decisions.
then this blog show how to make good decision http://www.marketingsecrets.com/images/rebootmethod/rebootmethod.html
Overconfidence is your biggest enemy: "A recently-published study by Brad Barber and Terrance Odean from the University of California found that overconfidence seems to play a key role in explaining why retail investors underperform when they switch from phone-based to online trading. This is the opposite to what one might expect given that 'straight-through' order processing is widely promoted as a positive development which leads to faster, more profitable trading results." http://www.wrenresearch.com.au/research/020902au/index.htm