Reviewing Past Stock Trades to Limit the Number of Future Mistakes

My trades span anywhere from a few days to several months. It makes sense that after I exit a trade, I evaluate the trade a month to three months later. By that time the charts will have produced enough information for me to identify what and why a trade resulted in a loss or gain (to a certain extent). Quantitatively, I determine if what occurred was just plain luck (probability wise – 50/50 chance a trade could have gone either up or down) or if it was something I consciously enacted and could have been prevented (given the conditions at the time) Basically I am looking to learn from my mistakes and more importantly not make them a second time.