Even negative moods serve a useful purpose. The emphasis we place on wanting to be happy all the time is misdirected and could even be damaging.
When Bobby McFerrin sang it back in the 1980s it was on everybody's lips: "Don't worry, be happy."
But being happy all the time might not be so good for us after all. Although we're often told of the benefits of being positive and upbeat, it appears there could also be plenty of plus points to feeling sad.
People who are down in the dumps are more attentive to their surroundings and less gullible than people who are happy, a University of New South Wales study found. The study also revealed that people who are feeling sad produce more effective and persuasive arguments than those in a positive frame of mind.
"People in a negative mood recall better memories, are better at detecting deception and are less likely to make judgmental errors," says study author Professor Joe Forgas.
"The study also revealed that sad people were more successful at communicating their thoughts than those in a good mood, less likely to believe urban myths and rumours and less likely to make decisions about someone purely based on their appearance."
Coping with challenge
But why does being sad give us the ability to make a good judgment call? "As humans evolved, moods came to be used as unconscious signals to inform people of the most appropriate way to process information," explains Professor Forgas. "A positive mood signalled, 'all is well, the situation is familiar', while a negative mood signalled, 'be alert and vigilant'. Therefore a negative outlook promoted a more attentive and externally focused, information-processing style."
Further research shows we may actually be subconsciously aware of the fact that a negative mood enables us to deal with challenging events more easily. People about to take part in an activity outside of their comfort zone, such as meeting and talking to a stranger, deliberately lowered their mood beforehand by reflecting on a sad memory or reading something sad, according to a study in the British Journal Of Cognition And Emotion.
Although Professor Forgas's study also shows the benefits of positive moods, such as creativity, flexibility and cooperation, he says it's important to focus on the fact that both a positive and negative frame of mind can be beneficial. As a society, we're bombarded with advertisements and self-help courses that portray the ideal state of mind as one of permanent happiness, but Professor Forgas reminds us this isn't the case.
"These findings suggest that all moods - even negative ones - serve a useful purpose," he says. "The strong cultural emphasis [we place] on wanting to be happy all the time is misdirected and could even be damaging. "It sends out a message that feeling negative is always unnecessary and dysfunctional, which is clearly not the case. Humans have evolved to experience the entire repertoire of emotions, and we should accept that temporary negativity is part of a normal existence. By propagating a myth that uninterrupted happiness is possible and desirable, it makes people feel worse than they would otherwise."
Psychologist Lyn Everingham agrees: "It's important to recognise that it's completely natural to have both high and low moods. Life throws different things at us. It wouldn't be normal if you didn't feel sad or upset after you've had a bad day or something hasn't worked out the way you wanted.
"Being sad doesn't mean you aren't coping with a situation. In fact, embracing sadness for a short period of time can often be a good thing; it helps you think about and come to terms with whatever has upset you, so you can eventually move on and feel positive again."
However, you can't force yourself to be in a bad mood purely to help you become more critical or have a better memory. "The effects of negative mood are automatic and subconscious," Professor Forgas says. "People are normally unaware of the consequences of their mood. Intentionally manipulating your state of mind to feel sad just so you can gain a better memory or stop yourself being so gullible probably wouldn't work."
Professor Forgas says it's important to understand that the key to experiencing the benefits that come with feeling sad is ensuring your negative moods stay within a healthy boundary. "It's only during temporary, short-term low moods that the benefits are present," he says. "Once a negative mood becomes long-lasting and more intense, the benefits disappear and the costs become greater. Enduring sadness, such as depression, can have debilitating effects."
Dr Ginni Mansberg says it's important to distinguish between feeling sad and being depressed. "If your low mood starts to interrupt your normal routine and the way you normally function, it should ring alarm bells," she says. "Unfortunately there is no clear-cut test for depression. Severe depression can be easy to spot, as it can include symptoms such as finding it hard to get out of bed and feeling suicidal. But it's harder to diagnose mild to moderate depression."
The key to differentiating between whether you're simply feeling a little bit low and whether you're clinically depressed is to work out what's normal for you, Dr Mansberg suggests. "If you're usually a 'glass-half-full' type of person and you've been feeling miserable for a while, then it's worth seeing your doctor. Talking to someone else about how you're feeling can help determine whether you might need help dealing with your low mood."
If you've been feeling sad for a while and the emotion is getting too much, there are things you can do to boost your mood. "Research shows that 30 minutes of exercise a day is as effective as a mild antidepressant," Dr Ginni Mansberg says.
"Some research also suggests that simply talking to your doctor about the possibility of going on antidepressants can help you feel better almost immediately - even if you don't actually get a prescription. Sometimes just discussing your problems can help."
The natural supplement St John's wort is thought to help relieve mild to moderate depression, Dr Mansberg says. "But you shouldn't take it if you're on the contraceptive pill as it can reduce effectiveness. See your doctor if you're concerned about your low mood."