"I'd be a burden"
As an example, say you move flat on your own, over a weekend, with a hired van. A friend hears about it afterwards and says "you should have said, I'd have come over". You thank her, and you privately mark it down as politeness.
Of all the beliefs in this book, this is the one I have most sympathy for, because it comes from something good. You notice other people's loads. You know your friends are tired and busy. Adding to that feels selfish, and managing alone feels like consideration.
Before any research, try a reversal. Think of the last time someone you like asked you for help. Perhaps a friend wanted a hand with a move, or a colleague asked your advice on something you know about. Recall how you felt when they asked. For most people the honest answer is somewhere between "fine" and "quite pleased". Being asked tells you that someone trusts you and thinks you're capable. You probably didn't think "what a burden she is".
If that's how it was, you're holding two rules. When others ask you, it's normal and even nice. When you ask others, it's an imposition. Both can't be right, unless other people are a more generous kind of creature than you are, and I doubt they are.
The research says the same. In 2022 Xuan Zhao and Nicholas Epley published a set of experiments with over two thousand people. In one, visitors to a botanical garden asked a stranger to take their photo. Before asking, they predicted how the stranger would feel, and afterwards the strangers were asked. The askers underestimated how willing the helpers would be. They underestimated how good the helpers would feel afterwards. And they greatly overestimated the inconvenience. On a scale from nought to ten they guessed about three, and the helpers reported about half a point. Three quarters of the askers thought the stranger had agreed partly because they felt unable to say no. Two per cent of the helpers said so. Other experiments in the set found the same pattern among friends.
That adds something to chapter 3. The explanation there was that people agree because refusing is awkward. In the garden the askers overestimated that awkwardness, and the helpers mostly said they'd wanted to help. I take both to be true. Reluctance to say no is part of why people agree, and it looks like the smaller part.
A photo is a tiny favour, and the helpers were describing their own feelings, so don't stretch this too far. It does fit a wider body of work suggesting that doing things for other people tends to lift the mood of the person doing them. The best-known finding of that kind, that spending money on others makes people happier than spending it on themselves, held up in a large repeat study in 2020, though the effect was small.
My own reading is this. Helping gives people something. They get to feel useful and trusted, and closer to you afterwards. If you never ask, the people around you never get that from you. They're left with a friend who'll do anything for them and lets them do nothing back, and that's a less comfortable position than you might think. Chapter 6 comes back to it.
An honest objection is that some requests really are burdens and some people really are stretched to their limit. A friend with a three-week-old baby isn't the person to ask for a lift to the airport. That's true. But it's a question about who to ask and when, and the belief treats it as a reason never to ask anyone.
For everyone who isn't obviously overloaded, I'd put it like this. You can't see into their week. They can. When you decide on their behalf that they couldn't manage it, you're making a decision that belongs to them, and there's a quiet unfairness in that, because it assumes they're unable to say no for themselves. Your part is to make the request clear, keep it a sensible size, and make it easy to decline. Whether they can spare the time is theirs to judge.
Notice, too, how small most of your unmade requests are. When you did the exercise in chapter 2, I expect most items were ten-minute favours. A ten-minute favour is a very small load to put on an adult who likes you.
One caution, which I also gave in chapter 1. The ordinary worry about putting people out is what this chapter is about. A fixed conviction that you're a weight on everyone you know is different, and it needs a doctor.