Apparently the ancient Greek & Roman philosophers thought that the whole point of philosophy was to develop a "Philosophy of Life". Basically an overarching goal, and a strategy for attaining that goal. Irvine has recently adopted Stoicism, or at least his own particular brand of Stoicism, as his philosophy of life and has written this book to help anyone else who wants to do something similar.
The Stoics' ultimate goal was to attain virtue, thereby achieving "tranquility", a psychological state marked by the absence of negative emotions. When you're in a state of tranquility it is easy base our decisions on logic rather than emotion, and lead a more virtuous life.
In order to achieve tranquility, the Stoics advocate several techniques. The first is negative visualization -where you imagine what would happen if you were to lose something you value; your job, your house, your partner, your child, your health. The goal of this is to help you appreciate what you have, as well as develop strategies to cope with a tragedy should it occur. The second technique is to stop worrying about things over which you do not have complete control, and to reframe your goals so that they are under your control. For example, if your goal in playing a game of tennis is to win, this will be affected by how well your partner plays. If instead your goal is to play your best, you can achieve this even if you don't win the game. Finally, the Stoics give a lot of fairly specific advice about how to deal with insults, cope with grief, and avoid envy.
The goal is to attain virtue or tranquility, not wealth. Stoics didn't have a problem with being wealthy, and certainly advocated enjoying your wealth and the things money could buy if you happened to have it, but recommended that you not become too attached to possessions.
Irvine goes into the history of Stoicism in a bit more detail, talking about several eminent Stoic philosophers, specifically Seneca, Epictetus, Musonius, and Marcus Aurelius. He also spends rather a lot of time worrying about how to cope with other people's opinion of your new Stoic lifestyle, and advocates not actually telling anyone that you're converting to Stoicism, which I found pretty hilarious. I suspect his target audience is relatively wealthy and running happily along on the hedonic treadmill, where you just keep buying more and better and fancier things in an attempt to make yourself happy. Their friends are all still on this treadmill and are going to give them a hard time if they don't acquire the latest gadgets and fanciest cars available, or wear clothing that is out of style.
While I was a bit irritated by the approach Irvine takes, since it is aimed at someone with a lifestyle very different than mine, I really appreciate his description of the Stoic philosophy of life. I had already adopted a lot of the strategies they advocate, but I think that doing them deliberately will help. I've been working to reframe my goals in terms of things I have control over (having a goal of getting my advisor to praise me is just silly...and hasn't been getting me anywhere). I really like the idea that I should be happy with my life, and that I don't need a giant pile of money and things. Helps to validate the decisions we've made over the past few years which overall I'm very happy about, but occasionally get pangs of envy when we visit friends who have made drastically different decisions, and now live in fancy houses with cars and gadgets and jet-setting lifestyles.