Have you ever noticed how we have a bad habit with the hard things we haven’t started yet? We stand at the bottom and stare up. We guess at how much it will cost us, how long it will take, how badly it might go.

And more often than not, the guess is wrong in one direction: too high.

That’s what I keep coming back to when I read this line from Dag Hammarskjöld. It’s a small saying but it names something that decades of research on how we predict our own futures keeps confirming: we overestimate how big the hard thing will be.

A quick note before I go further: I’m not a psychologist, and this is reading and reflection on the research, not advice. The studies here describe broad tendencies across groups of people. They aren’t verdicts about you, your goals, or how any single climb of yours will feel.

The man behind the line

Hammarskjöld wasn’t a self-help writer. He was a diplomat. He served as the second Secretary-General of the United Nations from 1953 until he died in a plane crash in 1961, on his way to negotiate a ceasefire during the Congo crisis. He was posthumously awarded the Nobel Peace Prize, the only time it has been granted after death.

The mountain line comes from somewhere much more private. It appears in Markings, a spiritual journal he kept for himself and never published while alive. It surfaced only after he died, translated into English by Leif Sjöberg and W.H. Auden in 1964. This isn’t a statesman lecturing about summits he’s conquered. It reads as a note-to-self, the kind a person writes while still at the bottom of most of their mountains, guessing at their height like the rest of us.

What the metaphor is really saying

Hammarskjöld isn’t talking about the mountain at all. He’s talking about how big a challenge looks to someone who hasn’t started. From the valley, the thing looks impossible, and that impression feels like fact. It isn’t.

It’s a forecast made by someone with no data, about a future version of themselves who doesn’t exist yet: the version who will have done the climbing, learned the route, and grown stronger on the way up.

So his advice is a warning against trusting the measurement you take from the ground. Start climbing. The size you gave the mountain from below was probably never right.

Why we’re so bad at measuring from the base

The psychology backs the poetry here.

There’s a well-studied habit of mind called affective forecasting: our attempts to predict how future events will make us feel. Psychologists Timothy Wilson and Daniel Gilbert found that when people imagine a future event, “they overestimate how powerfully the event will impact their emotional lives.” They call it the impact bias, and it runs both ways.

In one often-cited study, sports fans overestimated how happy a team’s win would make them and how long that happiness would last, an effect first reported in Wilson and colleagues’ experiments with college football fans. The same overshoot shows up with things we dread. We brace for a difficulty as though it will flatten us, and it usually doesn’t, because we forget how quickly we adapt and cope. This is one strand of research, not the last word, and the researchers are careful to say people tend to mispredict, not that they always do. But the tendency is real, and to me it’s the kind of error Hammarskjöld is describing. From the base, we measure a mountain we’re too frightened of to have climbed, and we do the frightening on behalf of a self who would have handled it fine.

The shrinking summit

Then there’s the second half of the line, the part where the mountain turns out to be low. Anyone who has finished a big thing knows the odd flatness that can follow. You expected to feel transformed. Mostly you feel like yourself, plus a finished task.

The author Ben-Shahar has a name for that letdown: the arrival fallacy, the belief that hitting a goal will bring lasting happiness. As one summary of the idea puts it, “upon meeting a goal, you will initially feel delighted,” but very quickly you drop back to your usual level of happiness, or even feel empty. That’s a popular account of the idea rather than a single measured result, so I’d hold it loosely. But it maps neatly onto Hammarskjöld: reach the top, look back, and the peak that loomed so large from the valley now looks modest.

The trap is thinking that shrinkage means the climb didn’t matter. It usually means the opposite. What I take from the line is that the summit was never the point. The person you became getting there is what’s left when the view stops impressing you, and that’s the part that lasts.

Starting before you’ve measured

If there’s a way to put this to work, it might be this: distrust the height you calculate from the ground, and start climbing before you’ve finished measuring. The estimate is coming from the person least equipped to make it, the one who hasn’t taken a single step and can’t yet imagine who they’ll be halfway up.

There’s a quieter reason to start, too. The palliative-care nurse Bronnie Ware wrote down the regrets she heard most often from dying patients, in a post that was read by more than three million people worldwide in its first year, before it became a book. The one she says came up most was this: “I wish I’d had the courage to live a life true to myself, not the life others expected of me.” The regret at the end isn’t usually about mountains that turned out taller than expected. It’s about the ones people talked themselves out of attempting at all.

If any of this stirs something heavier, about a life you feel you haven’t started living, a good counsellor or therapist is worth talking to.