Why you should sleep on it before making an important decision

Conventional wisdom holds that people are easily seduced by first impressions, and there’s solid scientific evidence that initial snap judgements are hard to shake—even when they turn out to be inaccurate.

But according to a new study, sleeping on it can help us avoid judging a book solely by its cover.

In research published in the Journal of Experimental Psychology: General, a team of researchers started with an age-old question. Is it better to rely on first impressions or on a more considered judgement?

To shed some light on the issue, they did a study involving an imaginary garage sale. In a series of experiments conducted online, the researchers asked participants to look through virtual boxes of unwanted goods for items to include in the sale.

Most of the items inside each box weren’t worth much—an old alarm clock, for example, or a potted plant. A few special objects, like a nice lamp or a teddy bear, were worth more.

The participants earned real cash based on the boxes they chose, so they were motivated to figure out which boxes were most valuable. Unbeknown to the participants, however, the combined total value of the 20 items in each box was the same. It was the sequence of the “junk” versus the “gems” that varied.

In some of the boxes, all the valuable items were on top, so as the participants unpacked the box, they spotted those items first. Other boxes had their valuable items clustered in the middle or at the bottom, and in some boxes they were intermixed.

After the participants had opened the different boxes, the researchers asked them to estimate the value of each one and choose their favorites. Some participants judged the boxes immediately, but others “slept on it” and decided after an overnight delay.

A pattern quickly emerged: When the participants had to decide right away, they tended to remember and judge boxes not by the entirety of their contents, but rather by the first few items they came across.

What the researchers say: “We found that people are strongly biased by first impressions,” the lead author said

Over and over again, the participants went for boxes with valuable items on top. When they spotted these “treasures” first before the low-priced items, they were more likely to pick that box than if they had seen the cheap stuff first.

Not only did the participants consistently go for the boxes that “started strong” over the others, but they also tended to overestimate their value—guessing they were worth 10% more money than they actually were.

This is an example of a psychological phenomenon called primacy bias the researchers noted.

When it comes to forming an overall opinion of something, it turns out we are unduly influenced by the first information we encounter, even when new facts come to light.

In the case of the garage sale experiment, this bias prevented participants from comparing the boxes rationally, and even led them to believe that some boxes were more valuable than they really were. At the same time, ironically, they were less able to recall specifics when asked which items in these preferred boxes were the “treasures.”

However, participants who weren’t asked to decide until the next day were less likely to fall into these traps.

“They made more rational choices, equally favoring boxes with clusters of valuable items at the beginning, middle, or end,” the researchers explained. Participants who “slept on it” no longer overwhelmingly preferred the boxes that made a good first impression. Boxes that saved the best for last were weighted equally favorably in their mental calculus.

"Judging from first impressions may actually be a good thing for choices in the moment," the lead author said. “Say you’re watching the opening scene of a movie or skimming the first few pages of a book. Quick snap judgements based on these initial impressions can help us decide when it might be better to move on before we invest too much time and effort.

“But when it comes to situations with longer-term stakes—for example, going back to a restaurant, or hiring or dating—there's wisdom in the idea of ‘sleeping on it’ before making a decision.”

“This is an exciting first look at how our brains summarize a rewarding experience," the lead researcher added. "When it's over, our brain knits it all together in memory to help us make better choices—and that neat trick happens overnight.”

So, what? This research needs to be replicated since it flies in the face of a lot of earlier research on the primacy bias and other elements of decision making.

These prior studies have shown that “instant” or “gut” decisions are about 60% more accurate than “considered” ones. Worst of all, according to these earlier studies, are those decisions where we take time to “weigh the pros and cons” of a particular course of action.

The primacy bias enables us to make very quick decisions and thus preserve our lives when faced with an emergency such as being confronted with a hungry lion or leopard. In such cases delay can be fatal.

Many studies have indicated that we may in fact make all our decisions very quickly (in less than five seconds) and only become conscious of the decisions we have made when we take time to justify them.

Then there is the school of thought among scientists which maintains that we never make conscious decisions at all—that we have very limited, if any, free will in decision-making. The way these researchers tell it we never make rational decisions—that is our decision-making is never based on facts or reason but instantly on the basis of emotion and/or the perceived need for relationship support.