We mistakenly conclude that we will feel tomorrow as we feel today

You’ve had an awful day—the cat peed on the rug, the dog peed on the cat, the washing machine is busted, World Wrestling has been preempted by Masterpiece Theatre—and you naturally feel out of sorts.

If at that moment you try to imagine how much you would enjoy playing cards with your buddies the next evening, you may mistakenly attribute feelings that are due to the misbehavior of real pets and real appliances ("I feel annoyed") to your imaginary companions ("I don't think I'll go because Nick always ticks me off").

Indeed, one of the hallmarks of depression is that when depressed people think about future events, they cannot imagine liking them very much.

Vacation? Romance? A night on the town? No thanks, I'll just sit here in the dark.

Their friends get tired of seeing them flail about in a thick blue funk, and they tell them that this too shall pass, that it is always darkest before the dawn, that every dog has its day, and several other important cliches. But from the depressed person's point of view, all the flailing makes perfectly good sense because when she imagines the future, she finds it difficult to feel happy today and thus difficult to believe that she will feel happy tomorrow.

We cannot feel good about an imaginary future when we are busy feeling bad about an actual present. But rather than recognizing that this is the inevitable result of the Reality First policy, we mistakenly assume that the future event is the cause of the unhappiness we feel when we think about it.

Our confusion seems terribly obvious to those who are standing on the sidelines, saying things like "You're feeling low right now because Pa got drunk and fell off the porch, Ma went to jail for whupping Pa, and your pickup truck got repossessed—but everything will seem different next week and you'll really wish you'd decided to go with us to the opera."

At some level we recognize that our friends are probably right. Nonetheless, when we try to overlook, ignore, or set aside our current gloomy state and make a forecast about how we will feel tomorrow, we find that it's a lot like trying to imagine the taste of marshmallow while chewing liver. It is only natural that we should imagine the future and then consider how doing so makes us feel, but because our brains are hell-bent on responding to current events, we mistakenly conclude that we will feel tomorrow as we feel today.

Daniel Gilbert, Stumbling on Happiness