When people try to imagine the more distant future—that classic interview question, “Where do you see yourself in 10 years?”—they tend to rely heavily on something called a cultural life script. This is the progression of events that a life in a certain culture is expected to contain. In much of the West, the cultural life script is something like: go to school, move out of your parents’ house, get one or more college degrees, find a job, fall in love, get married, buy a house, have kids, retire, have grandchildren, die. Not everyone expects their life to contain all of those events, but they’re aware of those milestones and will generally tell their life story using them as a framework. The further into the future you try to imagine, the more unknowns there are, so people reach for these events.

“We can’t really imagine or think that far into the future, and we can’t remember that far back, if we don’t have this cultural life script as a kind of skeleton for our life story,” says Annette Bohn, a professor of psychology at Aarhus University in Denmark. In studies Bohn has done with adolescents, their conception of a script seemed to develop in parallel with their ability to remember the past and imagine the future. (At the other end of the life course, older people’s ability to imagine the future declines in tandem with their memory.)

It’s not hard to see how this ability to imagine the future gives humans an evolutionary advantage. If you can plan for the future, you’re more likely to survive it. But there’s are limitations as well. Your accumulated experiences—and your cultural life script—are the only building blocks you have to construct a vision of the future. This can make it hard to expect the unexpected, and it means people often expect the future to be more like the past, or the present, than it will be.

In a similar vein, people tend to underestimate how much their feelings and desires will change over time. Even though they know that their personalities have changed a lot in the past, they have a tendency to think that the person they are now is the person they will be forever. This applies more broadly, too. You can see it in the technological advances imagined in science fiction. As my colleague Adrienne LaFrance wrote, while Back to the Future II (made in 1989 and set in 2015) made a lot of canny predictions—it got videoconferencing and drones right—it also thought people would still be using pay phones and fax machines. Which makes sense, given how ubiquitous those technologies were at the time the film was made.

There’s also an “optimistic, extreme positivity bias toward the future,” Bohn says. To the point that people “always say future events are more important to their identity and life story than the past events.” Talk about being nostalgic for the future.

But it might help people temper their expectations if they keep in mind that even though they can dream up detailed, novel scenes of things yet to come, their imagined futures are really just projections of their pasts. The future holds more surprises—and, potentially, more disappointments—than we might predict.