The decision
Up to now this book has asked you to notice things and to try one sentence. This chapter asks you to decide something. It comes this late because I wanted you to see the reasons first. Without them a rule like the one below is only gritted teeth, and gritted teeth last about a fortnight.
The decision is this. Nothing that will cost you more than an hour gets an answer in the moment.
It has six parts.
The hour. Small things carry on as before. Passing the salt, holding a door, giving someone a lift when you're going that way, reading a colleague's two-paragraph email before they send it. Say yes to those as freely as you always have. They're most of what makes you pleasant to be around, and they cost little. The rule only applies when the thing would take more than an hour of your life, or when it has no end date, like a committee. If you can't tell how long something will take, assume the rule applies to it.
The holding line. For anything over the hour, whoever asks and however nicely, you say, "Let me check and come back to you," and you name a time. You say it even when you think the answer will be yes. That way it becomes what you always say and doesn't signal that a no is coming. You'll be glad of that when it's your manager asking.
The check. At home, or at your desk once they've gone, you do three things. You move the date to tomorrow and ask whether you'd say yes. You picture the slip of paper with its two boxes. And if it's close, you ask the questions from chapter 10. Who's asking, what does it cost, what is it for, and would I be glad afterwards? This takes a few minutes. Most cases are clear inside one.
The answer. You reply by the time you said you would, in writing if that's easier. A yes should be a proper one, with the date in your diary. A no should have the two or three parts from chapter 13. Either way, you keep your word about coming back.
The policies. Some evening this week, write down the three or four kinds of request where your considered answer is always the same, as in chapter 6. Keep the list where you'll see it. These requests don't need the holding line, because the checking has been done.
The yeses already given. Look at the next two months in your diary and find the unwilling yeses already in there. My advice is to honour most of them. You gave your word, people have planned around it, and pulling out late does the damage described in chapter 8. Do them as well as you can and let them be the last of their kind. The exception is the commitment with no end, such as the committee seat, the weekly lift or the rota you never chose. For those, send one clear message with a date in it. "I'm going to step down from the committee after the September meeting. I wanted to give you plenty of notice." That gives them time to replace you, and it's fair to everyone, including you.
It helps to decide in advance what you'll do at the difficult points. There's a well-tested way to do that, a plan in the form "when this happens, then I'll do that". Peter Gollwitzer and Paschal Sheeran pooled 94 tests of plans like this and found they made people a good deal more likely to follow through. Here are three I'd suggest. Change the wording to suit you, and say them aloud once.
When someone asks me for something that would take more than an hour, then I'll say, "Let me check and come back to you tomorrow."
When someone presses me to answer on the spot, then I'll say, "If you need to know now, it's a no."
When I sit down to reply, then I'll move the date to tomorrow before I do anything else.
Here's what to expect, and I'll be careful because I can't promise you an outcome. The first few nos will feel bad, even by message. Your heart will go a bit as you press send. You may check your phone more than usual for the next hour. Then a reply will arrive, and in most cases it will say something like "No problem, thanks for letting me know". After a few of these the dread gets smaller, because your forecast is at last being corrected by evidence. Some replies will be cooler than that, and chapter 15 covers those. You'll also still say the odd "yes, of course" at the bins, and chapter 15 covers that too. What I'd expect after a couple of months is a diary with fewer things in it that you dread, and an easier conscience about the ones that remain.