A fool doesn't learn from his mistakes. An average person does. But the wise man learns from the mistakes of others. Jim Paul tells you about his mistakes in What I learned Losing a Million Dollars, in the hope that you will not commit the same ones.
I found the first part of the book interesting, as Paul discusses the key events and situations that shaped his career. He went from being a golf caddy as a teenager to being a high-rolling commodities trader. But he blew himself up (financially), and blames it on the fact that he had been so successful that he wasn't paying enough attention to his downside.
I think Paul is absolutely right in his assessment. Nothing breeds overconfidence like success, and the result is often dramatic failure.
Paul then goes on a dive into psychology as it relates to finance. If there wasn't a whole field of behavioural economics already, this part may have been fascinating. But as it was, it felt rather incomplete and disjointed compared to what's out there already from guys like Kahneman and Thaler.
Finally, Paul offers the practical advice from all this, which is to have a plan *before* you make an investment. This prevents your emotions from keeping you in losing positions for longer than you should be. In Paul's case, this means use a stop-loss right from the start. I'm not sure this applies very well to value investors, who welcome price drops for the opportunity to buy more. Nevertheless, I think the idea of having the downside exit plan before investing is still a sound idea, even if it doesn't have to be in the form of a stop-loss. For example, if a thesis is based on returns on capital as a result of a strong moat, a plan may require an exit if capital returns cross a certain threshold on the way down, whereas if there were no plan an investor may convince himself to hang around until the stock price gets back to even, for psychological reasons.
If you want to learn from the mistakes of others, What I Learned Losing A Million Dollars is as good a place as any to get started.