The chapter entitled, "More Thoughts on Human Nature and Speculation", includes some classic thinking on aspects of human psychology which prevent us from operating profitably in the markets. A passage from Neil on the dangers of greed follows this line of thought:
"...I have watched traders in brokers’ offices with deep interest, and have tried to learn the traits that crippled their profits. The desire to “make a killing”—greed—has impressed me particularly.
Perhaps this desire to squeeze the last point out of a trade is the most difficult to fight against. It is also the most dangerous. How often has it happened in your own case that you have entered a commitment with a conservatively set goal, which your judgment has told you was reasonable, only to throw over your resolutions when your stock has reached that point, because you thought “there were four more points in the move?”
The irony of it is that seemingly nine times out of ten (I know, for it has happened with me) the stock does not reach your hoped-for objective; then—to add humiliation to lost profits—it goes against you for another number of points; and, like as not, you end up with no profit at all, or a loss.
Maybe it would help you if I told you what I have done to keep me in my traces: I have opened a simple set of books, just as if I were operating with money belonging to someone else. I have set down what would be considered a fair return on speculative capital, and have opened an account for losses as well as for gains, knowing that the real secret of speculative success lies in taking losses quickly when I think my judgment has been wrong.
When a commitment is earning fair profits, and is acting as I had judged it should act, I let my profits run. But, so soon as I think that my opinion has been erroneous, I endeavor to get out quickly and not to allow my greed to force me to hold for those ephemeral, hoped-for points. Nor do I allow my pride to prevent an admission of error. I had rather, by far, accept the fact that I have been wrong than accept large losses..."
This looks like worthwhile study material, so read on and don't mind the fact that most of the references date back to 1930. Time honored wisdom is the best, and sound practices are applicable in any age.