I spent all weekend reading this book and can't recommend it enough for day traders.
My biggest takeaway was around the sunk cost fallacy and continuing to invest in the hopes that a loss can be recovered. At one point in the book, she suggested that sticking to a trade would be the same as buying into the trade, and if you wouldn't buy into it at the given moment, then you shouldn't stick to it.
She also hammered home the concept of kill criteria. Specific triggers that indicate your goals are unlikely to be met, making the decision to exit easier.
I've found myself holding onto losers for far too long, and several concepts in this book really hit home.
Some highlights are summarized in the link below, but IMHO the book is worth the time for a full read.