"I'm only being realistic"

The strongest defence of the dip is that it's honest. You looked at the evidence, the evidence said you're behind, and refusing to see it would be a comfortable lie. If that's how it seems to you, I'd like to look at the evidence.

Start with where it comes from. You see other people when they're with other people. You see them at dinners, at work, at the school gate and online. You almost never see them alone at the kitchen table with a letter from the bank. You're present for every minute of your own life, including all the minutes nobody else will ever hear about.

In 2011 Alexander Jordan and five colleagues published four studies on this, all with students at one American university. In the first, 63 students described recent times when they'd felt bad and times when they'd felt good. About 29 per cent of the bad experiences had happened with nobody else present, against 15 per cent of the good ones. The students said they'd tried to hide 40 per cent of their negative emotions from the people who could see them. For positive emotions the figure was 13 per cent.

The next study asked 80 students to estimate how many of their peers had recently been through those same experiences, such as a distressing argument or feeling sad about missing home. They underestimated how common the bad experiences were. Their estimates for the good experiences weren't out in the same way.

So the students' bad moments tended to happen in private and their good ones in company, and the bad ones in company got hidden. As a result, each student concluded that other people were having fewer bad moments than they really were.

It's a bit like judging a country's weather from its postcards. Every postcard is a real photograph of a real day. Nobody is lying to you. But nobody prints a postcard of the rain.

You may think this applies to acquaintances, and that your real friends tell you the truth. The third study followed 214 students through a ten-week term. They logged their emotions weekly, and at the end each named up to three people who knew them well, mostly friends, roommates and partners. Those close peers still underestimated the students' negative emotions and overestimated their positive ones. Part of the gap was explained by how much the students said they suppressed their bad feelings. Even your friends are showing you a selection. They don't mean to deceive you. "How are you?" is a greeting, and "Good, thanks" is what people say back.

The fourth study is the one that bears on the dip. Among 104 students, those who gave lower estimates of other people's bad experiences reported more loneliness and more brooding, and lower satisfaction with life. That's a correlation from a single survey, so it can't show which causes which. It does fit what you'd expect. If you think you're the only one struggling, the struggle gets heavier.

These were American students, mostly in their first year, and I can't prove that the figures carry over to adults with mortgages. I'd be surprised if the direction were different. Adults have had longer to practise saying "Good, thanks".

Notice what this doesn't say. It doesn't say your friend is secretly unhappy. Nothing at the housewarming was fake. The kitchen is real, the promotion is real and the children really did say please. What persuades you about other people's good bits is that they're true.

The mistake is about what's missing. You saw four hours, chosen and prepared, and treated them as a fair sample of a life. Then you compared that sample with something that wasn't a sample at all.

So here's the question I'd like you to start asking when the dip comes. What didn't I see? You don't have to answer it. You certainly don't have to invent a hidden misery for your friend, which would be a different mistake and a slightly mean one. The question only marks the evidence as partial, and partial is what it is. You'd do the same with any other report that had half the pages missing.