A University of New South Wales psychology researcher has found that grumpy people think more clearly than happy people, according to the BBC:

In contrast to those annoying happy types, miserable people are better at decision-making and less gullible, his experiments showed.

While cheerfulness fosters creativity, gloominess breeds attentiveness and careful thinking, Professor Joe Forgas told Australian Science Magazine.

The University of New South Wales researcher says a grumpy person can cope with more demanding situations than a happy one because of the way the brain "promotes information processing strategies".

So when I get all gloomy because I can't come up with a creative solution to a problem, I can carefully and attentively implement a not-so-creative solution. Well, better than nothing, I guess.

Of course, this bloke is an Aussie, so his whole worldview is upside-down.