In April this year, scientists from Georgia Tech and Yahoo Labs reported that something strange was manipulating online restaurant reviews. It wasn't hackers. It wasn't software bugs. It was rain, snow, and sunshine.

After looking at more than 1 million online reviews on sites like TripAdvisor, they found that restaurants received significantly better ratings on days with nice weather and worse reviews on any day with rain. “The best reviews are written on sunny days between 70 and 100 degrees,” researcher Saeideh Bakhshi concluded. “A nice day can lead to a nice review. A rainy day can mean a miserable one.”

In short: Yelp reviews are accidental weather reports.

A low-pressure movement pushing cumulus clouds above a certain zip code should not affect the seasoning of a steak served there. It does, however, affect a person's mood. It shapes how the individual feels when he enters the restaurant, confronts the host, consults with the waiter, tastes the steak, and grabs his umbrella to leave. Research going back decades has consistently shown that cloudy weather puts people in a huff, and huffy patrons leave worse reviews.

This isn't just another reason to distrust restaurant criticism. It's a reason to distrust ourselves. Far from rational consumers, most people are unwitting servants of fleeting moods.

Before continuing, I'll acknowledge that moods might seem like an unsophisticated subject for serious research. They strike at random and often pass in minutes. People typically shrug them off, along the lines of "oh I'm just in a bad mood," or "my boss is in a weird mood."

But the reason moods matter is precisely that they are so present. Since humans are terrible at thinking about the future, they make lots of decisions on the basis of how they feel, here and now, rather than how they're likely to feel in the future. New Years puts a person in a forward-thinking mood, which results in hundreds on a gym membership. Birthdays encourage thinking about today, which licenses indulgence.

Moods, despite their short lifespans, shape a person's attention, his entertainment, and his choices.

Negative moods can lead to a procrastination doom loop, in which an individual perpetually delays important tasks while waiting for an angel of inspiration to visit. Negative moods can lead to other doom loops, too. Optimistic and happy people are associated with higher incomes, more successful social interactions, and longer lives. Does the physical experience of happiness confer magical health benefits? Perhaps. But a popular explanation for the happy and successful is that positive moods can make the person exquisitely sensitive to rewards in an environment. A good mood heightens the benefits of going to the gym, eating raw kale, and doing favors for friends. A foul mood makes the individual exquisitely aware of all the downsides of these activities—the sweat, and bitterness, and the hours hauling couches up flights of stairs.

But there are some moderate upsides to bad moods: They heighten attention to detail. “If attention is like a spotlight, then a good mood will widen that spotlight, while a negative mood will focus it very tightly,” said Adam Anderson, assistant professor of psychology at the University of Toronto. If attention is a filter, good feelings widen the mouth, opening up to all sorts of stimuli, which helps with free association and creativity. But "that kind of broad or diffuse attention can be detrimental in situations that demand a laser-like focus,” Anderson said. Positive moods inspire faster and more creative thoughts, but fast thinking isn't always suitable for every task. For this reason, if a day includes both brainstorm sessions and Excel work, science would advise playing happy music before the group session and transitioning to a moodier fare for the detail-heavy work.

Moods can also determine the sort of products that a person finds interesting. A recent study in the Journal of Consumer Psychology investigated how happiness affects consumer choice. There are two main flavors of happiness, the researchers said: a present-based happiness, which feels like calmness, and a future-based happiness, which feels like excitement. These flavors evolve as a person ages. One study of 70,000 instances of happiness on blogs showed the meaning of happiness evolving over time from excitement when people are young to peacefulness when they old.

In one of their studies, Cassie Mogilner and other researchers primed participants to think about the future or the present with word scrabbles. Then they were offered two brands of water, one called Pure Calm and one called Pure Excitement. Prompting consumers to think about the here-and-now made them significantly more likely to prefer a product that promised calmness.

Hunting for Happiness: Now and Later

Mogilner et al

Finally, moods shape media consumption and consumers' appetite to be challenged by new entertainment.

Norbert Schwarz is one of the country's top psychologists studying metacognition, or the "feeling of thinking." Across a range of subjects, he says, most people are attracted to stimuli that are easy to process—like familiar names, symmetrical designs, and simpler melodies—because people conflate the ease of thinking with quality and comfort. This is especially true, Schwarz told me, when people are in a foul mood. "When you’re in a bad mood, you want to see your old friends," he told me, "not meet new people. When you’re stressed out, you’re not putting on the new movies. You want the [TV] re-runs. They relax you."

When Jonah Peretti founded BuzzFeed, he declared it was for the "bored at work" crowd, which is, almost by definition, floundering in foul moods. "Sad moods signal problematic environments that enhance [our] appreciation of familiar and safe stimuli," Schwarz wrote in his review of metacognition. No wonder some of BuzzFeed's most popular stories are so familiar, they are practically mirrors held up to their readers (e.g.: What Friends Character Are You? 27 Things About Being 27). Say what you will about BuzzFeed, but it is clearly optimized for the attention mood of its audience.