This monograph reports the results of a large scale experimental study into the decision-making process, in particular into how repeated decisions on whether to buy or sell are made when trading stocks. It considers how the resources and the objectives of individuals influence their behaviour, the perception that success is the result of being active and aggressive in the market and how the decision-making process is often minimised by repeating the same basic decision. It also compares the evidence of the actual behaviour of individuals with financial theory.