After a bad one
At some point you'll lose your temper again. It may come after three good weeks, on a day when you were ill and the car failed its test and somebody said the one thing. I'm telling you this now so that when it happens you'll recognise it as a normal part of changing a long habit. It doesn't prove that the book was wrong or that you didn't want it enough.
What matters is the next hour. The old pattern after an outburst had two stages, a defence followed by shame, and neither helped anyone. Here's another sequence.
First, stop as early as you can. Stopping at minute three is better than stopping at minute ten, even though it may not feel that way. Every further minute adds things said that you'll have to repair.
Second, cool down the same way as before. Go for the slow breathing and the walk, and see the scene from across the room.
Third, repair it, and do it properly. A useful apology names what you did, in specific terms. "I shouted at you and I called you lazy. That was wrong, and you didn't deserve it." It doesn't include the word "but." "I'm sorry I shouted, but you know how I get when you ignore me" isn't an apology. It's the argument starting again. It also doesn't ask the other person to say it's all right. They may not be ready to, and they don't owe you that on your timetable.
Your original point, if you had one, doesn't disappear because you delivered it badly. It does have to wait. Bring it up separately, later, in the form from chapter 9. If you put the grievance and the apology in the same breath, they'll hear only the grievance.
If it was your children you shouted at, apologise to them too. Some parents worry that this weakens their authority. I'd say it strengthens it. A child who hears "I was wrong to shout, and I'm sorry. I was angry about the mess, and that's still something we need to sort out" is learning that a person can get angry and make a mistake and then put it right. Most of us never got that lesson as children.
Fourth, go over the episode calmly, and do it to learn from it. You aren't looking for reasons to feel worse. Work back through the chapters. What state were you in, in terms of sleep, food, drink and the day you'd had? What story were you telling yourself, and did it turn out to be true? What was the first sign, and when did you notice it? Could you have used the exit line, and if you didn't, what got in the way? Usually you'll find one specific weak spot, and it'll be something small and fixable like "I never have these conversations well after nine at night." That's much more use to you than "I'm hopeless."
A lapse doesn't put you back at the start. Everything you've understood is still understood, and every urge you sat through still counts. If anything a lapse shows you the conditions in which your method is weakest, so you can strengthen it there.
Now, trust. If you've had a temper for years, the people close to you have adapted to it, in the ways described in chapter 5. They won't drop those adaptations because you read a book and had a good fortnight. They may well be wary of the new calm and wait to see if it lasts. They may even test it, without meaning to. It can feel unfair when you're trying so hard. But a few weeks is a short record compared with years, and the only thing that changes their minds is time and consistency. Don't ask them for credit. If the change holds, they'll notice it for themselves.
Last, professional help. Seeing a professional is a sensible next step for many readers, and it's not a last resort. Anger is among the problems that respond well to treatment. Amy Lee and Raymond DiGiuseppe reviewed the existing meta-analyses of anger treatment in 2018. They found that psychological therapies, mostly cognitive behavioural therapy, produced at least moderate improvements fairly consistently, in ordinary adults and in people with psychiatric diagnoses alike. A course of that kind covers much of what this book covers, with a trained person helping you apply it to your own life, and with practice, which a book can't supply.
I'd urge you to seek that help if any of the following is true. You've been violent or threatening towards anyone, or you've broken things to frighten someone. People at home are afraid of you. Your anger has cost you a job or a relationship, or brought you into contact with the police. You have rages that seem to come from nowhere, or they've begun recently. You're also struggling with low mood, anxiety, trauma, or heavy drinking or drug use, all of which can show up as anger. Or you've given the approach in this book an honest few months and things aren't improving. Your doctor is the usual place to start, and they can also check for physical causes. If you ever feel you might seriously hurt someone or yourself, contact emergency services or a crisis line straight away.