For me, "trading in sample sizes" and "thinking in probabilities" are the two most vital takeaways from Douglas. Douglas's "Twenty Trade Exercise" is without a doubt the best cure I know for all manner trading errors, including over trading, letting losses run, cutting profits short, FOMO chasing, revenge trading, etc. It is both a discipline building exercise and an exercise in emotional detachment from the outcome of particular trades.
I think both of his books could have been shortened substantially. I do not know that Trading in the Zone added so much to his work. However, it did distill, focus, and, in my opinion, more clearly present the ideas he developed in The Disciplined Trader.
Many would probably have a much better opinion of Mark Douglas's Trading in the Zone if they would start with chapter 6, proceed to chapter 7, and then read and do the exercise outlined in chapter 11. This allows one to keep the baby while throwing out the proverbial bathwater.
