Go to UniverseUnboxed.com to learn about SciShow science kits, and stick around to the end of this episode to hear more about this exciting new SciShow project! [INTRO ♪].

You've probably had a friend tell you to, like, “look on the bright side” when something bad happens. Or, maybe you've heard someone say “happiness is a choice” or “if you believe it, you can achieve it." This idea that you can think your way to happiness, health, and success has been the topic of countless books, motivational speeches, meditation apps, and videos.

But it turns out, like with pretty much everything in psychology, the truth is more complicated. And thinking positively can sometimes backfire and make you feel worse. This idea that positive thoughts will manifest in your everyday life is so widespread now that it's almost gimmicky.

Like, you know those cheesy self-help books that have you repeat “I am strong, I am confident, I am worthy of love, and gosh darn it, people like me.” But the idea that our thoughts have power over our life hasn't actually been around for that long. The term “positive psychology”–which refers to any kind of psychological intervention that focuses on strengths and good qualities—was first cited in 1954. And the idea that thoughts can impact our health and well-being only started to gain scientific credibility in the mid 1980s with a study that found that people who were inclined to look on the bright side of life were less bothered by things like stress or muscle soreness.

In fact, the positive psychology movement as we know it today didn't really come about until the late '90s. The tenets of this movement quickly became adopted all over the place—from the business world, to the US military, and even some school systems—as a way to improve coping skills, performance, and mental health. And the rest, as they say, is history.

But for all the hype about positive thinking, the evidence for effectiveness is still pretty weak. A 2010 review points out that much of the research is correlational. Positive thinking has been associated with better health and longer life, for example, but that doesn't necessarily mean one causes the other.

There are a lot of other contributing factors that just aren't being captured by the current studies. And the causation could go the other way—after all, it would not be super surprising if being healthier made you see the world in a more positive light. Also, a growing body of research has shown that positive psychology can, ironically, be kind of negative.

When study participants are told to imagine a positive outcome, they often end up being less likely to achieve their goals. Research suggests that's because such positive fantasizing kind of kills your motivation. For example, researchers in a 1999 study found that undergraduates who focused on getting a higher grade on a test studied less, which resulted in a lower grade.

And in another study, participants that envisioned themselves getting their dream job ended up sending out fewer applications, and not surprisingly, getting fewer job offers. This isn't the only way positive psychology can backfire. A study done in 2009 found that repeating positive self-statements like “I am a lovable person” actually made people with low self-esteem feel worse.

The researchers suggested this might be because those mantras reminded them of all the ways they weren't measuring up. Instead of boosting their esteem, the statements seemed to lead the participants to dwell on why those positive phrases weren't true for them. And you might think that positive thinking would be most useful when life is really hard—like, if you were diagnosed with cancer.

But a 2010 review of positive psychology in cancer care found that attitude had no effect on survival. In fact, negative emotions tend to help people process chronic illnesses better. Psychologists think this could be because focusing on the positive becomes a form of denial, while feeling all those awful feels lets people deal with the realities of their situation.

And there are other times when it's helpful to take off the rose-colored glasses, because psychologists have found that we process information differently depending on how we feel. In short, your brain puts more effort into careful, thoughtful analysis of the world around you when you feel kind of crummy, because it's trying to figure out the best way to fix whatever you feel is broken. Studies have found that negative moods enhance systematic processing in your brain, for example—so being pessimistic can help you form stronger, more persuasive arguments and help you distinguish fact from fiction.

And pessimism can improve your memory, as studies have found that when you're in a good mood, your brain doesn't really take the time to distinguish important information from useless details. This is why I remember nothing. Negative moods can also help you avoid making mistakes, since processing all the worst-case possibilities can make you work harder to avoid those potential pitfalls.

So I guess just be pessimistic and sad! [laughs] No, that's not what we're saying. Positive thinking can work—sometimes. For example, a 2015 brain imaging study of 67 people found that self-affirmations based on the participants values activated the reward centers of their brains and motivated them to change their future actions.

But context really matters. For example, a 2012 study found that when you think people expect you not to feel sad about something, that actually makes you feel more sad about it. Researchers have also found that the effectiveness of positive thinking is dependent on individual factors like how anxious you are, your personality, your cultural background and belief system, and what kind of coping mechanisms you have.

Take that 2009 study, for example—the one that found that positive self-statements backfired for people with low self-esteem. It also found that they worked for people who had high self-esteem: those participants felt significantly better after repeating the mantras. And there's one group of people where positive thinking pretty much never works–they're called defensive pessimists.

They're the people who overthink everything and imagine all the things that could go wrong in a situation. And if that sounds like you? You're not alone—psychologists estimate as many as 30% of people may be defensively pessimistic.

As doomsday as this kind of thinking might seem, a number of studies have found that imagining all the worst case scenarios is a defensive pessimist's preferred coping style, and if you take that away, they're worse off. Their negative thinking makes them less prone to experiencing depression when something bad happens, like a friend dies, because they spend more time bracing for the worst. And their pessimistic outlook can also help motivate them to take control in situations, and strange as it might seem, it can boost their confidence.

But when they're forced to be optimistic, that damages their performance. So for some people, always looking on the dark side of life is actually better than trying to see that silver lining. It seems that, like with most things, there is no one-size-fits-all strategy for boosting self-esteem or dealing with all the terrible stuff life throws at you.

And if you think about it, you might already know what works best for you. If you feel like you're forcing yourself to think happy thoughts and it really isn't helping...you're probably right. But if repeating “I am a lovable person” brings you confidence and joy, go for it!

We're not here to yuck on your yums—we're just here to give you the facts. Before you go, we have a very exciting announcement. SciShow has just launched Universe Unboxed, our very own line of science experiment kits for kids elementary school-aged and older.

They're packed full of fun experiments which teach specific science concepts, and for each, there is a video demonstration featuring me! So you can see how it's done and guess what happened before you learn the science behind them. Like, in the “Brain Teasers” kit, you learn how to do some things that seem impossible, like fit an inflated balloon inside of a bottle.

Turns out you can't just put a deflated balloon in first and blow it up from the outside—and that has everything to do with how air and gas pressures work. In addition to explaining the experiments, we also explain how scientists actually use the scientific concepts you're learning in the real world. So you're not just learning how science works—you're learning why it matters.

To buy one of these kits for yourself or your favorite kid, or to find them in a store near you, check out UniverseUnboxed.com. [OUTRO ♪].