When I first picked up this book, I wasn’t sure if I would enjoy it. The introduction hit me with a couple sentences that gave me pause. First: “If you have never played poker before, the best course of action is to put this book down, read some of the other books in print aimed at beginners, play some poker, learn some more, and then return after gaining additional experience.” I have never played poker, and nor am I about to start. I wondered if I wouldn’t be able to follow the book. It was rough going for a while, since the book did not include even a basic overview of the rules of poker, nor was their a glossary for the substantial amount of poker jargon used. Poker tutorials online were also surprisingly bad. For example, one hold’em tutorial for beginners only said that rounds consist of checking, betting, and raising, without explaining how those actions may be used. I also learned that for any conceivable rules question in poker, the answer is “it depends on the variant.” In the end, I managed via a mix of googling and asking my husband questions, since he has played poker.
The second concerning sentence: “The primary goal of our work here is not to solve game theory problems for the pure joy of doing so; it is to enhance our ability to win money at poker.” Since my interests are the exact opposite, I thought maybe the book would not be for me. However, the approach was very careful and precise, exploring simplifications where optimal strategy could be derived completely. Some of the chapters got a bit too detailed for me to be interested in following, given that I'm not planning to apply them, but overall I found an incredible amount of joy in this book.
The biggest insight I got from this book is how fundamentally defensive Nash equilibria are. For example, consider a game of Rock Paper Scissors where the utility of winning with scissors is doubled. That is, if you win with scissors, you gain 2 points and your opponent loses 2 points. If you win with rock or paper, you gain 1 point and your opponent loses 1 point. If there is a tie, no one gains any points. I didn't pause to predict the result before reading on, but I might have expected the result would be that scissors is played more often. Instead, the Nash equilibrium is playing rock with probability 1/2, scissors with 1/4, and paper with 1/4. Why did rock increase? Because rock is the counter to scissors. The Nash equilibrium strategy usually makes your opponent indifferent between their options. To make the opponent indifferent to playing scissors when its utility increases, you have to play rock more often. At the same time, if the opponent is also playing the Nash equilibrium, you cannot gain utility by playing scissors more often. Your opponent has made you indifferent.
This concept applies to poker as well. For example, suppose you are playing limit poker, meaning there is one fixed bet size that is allowed. As the size of the pot increases, how should bluffing and calling behavior change? The answer is that you should bluff less and call more. This example was discussed in the book before the Rock Paper Scissors example, and I had a lot of trouble seeing why. After all, the utility of bluffing and calling both increase as the pot increases, so why should you do one less and the other more? The answer is that this is correct defensive play. The counter to bluffing is calling, so as bluffing gets better you call more. The counter to calling is bluffing less, so as calling gets better you bluff less.
Some other highlights for me: Chapter 7 discussed games with a made hand (who has the best hand currently on the board, e.g. a pair of aces) and a draw (who is trying to draw into a better hand, e.g. they currently have 4 card of the same suit and would like a flush). The draw often prefers to get all-in before more cards are drawn, going against my intuition that the draw would like to see more cards as cheaply as possible. This is because the made hand wants to preserve the option to make large bets in cases where the draw misses. Chapters 22-25 had some interesting analysis of how to play poker professionally without running too great a risk of losing all your money at some point. And Chapter 29 had some strange scenarios that can occur in 3-player games.
Finally, one big takeaway from this book for me was just how high a variance there is to poker. Whenever the authors put in numbers they thought were realistic assumptions as to how much of an edge a player might have, I was shocked by how easy it was to lose money despite being the best player. They gave one example of an overall winning player who nonetheless had a 45% chance of being down money after 300 hands! If I had any inclination to play poker before reading this, it completely vanished. It just doesn't sound fun to play a game where you need statistical analysis to know if you're doing well.