Self-confidence is a bit like the running water in your house. You may not know every detail about how it works or where it comes from, but it’s painfully obvious when it’s not there. Like when your water is shut off, a dearth of self-confidence has a huge negative impact on your health and lifestyle. Fortunately, there are things you can do to shore it up.

What is confidence?

In everyday conversation, self-confidence is often confused with self-esteem, and it overlaps with the less well-known term “self-efficacy.” However, psychology gives each of these terms a specific definition. It’s helpful to distinguish among the three:

• Self-Efficacy: This term, as defined by Albert Bandura, a Canadian-American psychologist, refers to your belief in your ability to accomplish specific tasks. If you believe you’re capable of cooking dinner or completing a project, this is reflective of high self-efficacy. People with low self-efficacy often put less effort into a task if they don’t believe they’ll succeed at it, increasing the likelihood of failure.

• Self-Confidence: In contrast, according to Dr. Bandura, self-confidence is more of a general view of how likely you are to accomplish a goal, especially based on your past experience. When you practice playing piano, you increase your confidence in your ability to play the piano. This can also apply to how likely you believe you are to be accepted in a social group. If you’ve been made fun of for your underwater basket-weaving hobby, you might be less confident sharing it with others next time. Self-confidence and self-efficacy are both rooted in experience, but self-confidence reflects a broader view of yourself, rather than your confidence in specific tasks.

• Self-Esteem: The term most often confused with self-confidence is the one perhaps least similar to it. Self-esteem refers to a belief in your overall worth. Broad statements like “I’m a good person” fall into this category. Self-esteem is one of the levels of Maslow’s hierarchy of needs, and improvements to self-confidence can contribute to your broader self-esteem.

These concepts overlap, and psychologists disagree about where the lines are between each one. You can have enough confidence to believe that you’re capable of learning how to play a new game, for example, while simultaneously lacking the self-efficacy to believe that you’ll be any good when you first start. Likewise, you can have zero confidence in your ability to cook while still believing you’re a good person and deserving of love.

High confidence leads to more chances to improve

Self-confidence is your belief in how good you are at something, but it’s not a measure of your actual skill. So why does it matter if you believe in yourself? According to Charlie Houpert, the author of “Charisma on Command” and the founder of a 2.7-million-subscriber YouTube channel of the same name, confidence doesn’t just make you feel better, it also helps you take risks to make tangible improvements to your life.

“Internally, true self-confidence will lead to more positivity, happiness and resilience,” Mr. Houpert said. “Externally, high self-confidence will lead to taking more risks, which directly correlates with reaping more rewards.”

The “Oxford Handbook of Positive Psychology” puts it another way: “If the person lacks confidence, again there will be no action. That’s why a lack of confidence is sometimes referred to as ‘crippling doubt.’ Doubt can impair effort before the action begins or while it is ongoing.”

If you believe you can get your dream job if you apply, there’s a chance, however small, you might get it. If you don’t believe that you can get it, and you don’t apply, it’s guaranteed that you won’t. Self-confidence doesn’t magically make you better at what you do, but it does prime you to take the risks necessary to achieve your goals.

How you can improve your self-confidence

If building self-confidence is a matter of changing your beliefs about yourself, it’s going to take some work. You can say, “I’m good enough, I’m smart enough and, doggone it, people like me” into the mirror every day — and it couldn’t hurt — but there are more practical, effective tools you can use, too.

Be ‘hyper honest’ with yourself

Mr. Houpert suggests being “hyper honest” with yourself as a simple, everyday way to exercise your confidence.

“For example, let’s say someone asks you what you do for fun or what you do for a living,” he said. “If you find yourself biting your tongue or hiding something, evaluate that. That’s an indication to either stop doing that thing or, more likely, accept that part of yourself and own it.”

This doesn’t mean you have to share every part of your personality with everyone you meet. You can share your geeky hobbies with your geeky friends but stick to work topics at work. However, you can find someone to share yourself with. “When you stop hiding parts of yourself from other people, you’ll find you feel more confident in who you are,” Mr. Houpert said.

Start working out

Many people start working out to lose weight or build muscle, but exercise can also be a huge boost to your self-confidence. The American Psychological Association has noted that exercise can improve your mood and — along with regular treatment and therapy — help combat depression and anxiety. It can also help improve your confidence if you stick with it for a while. Working out regularly requires a commitment, and keeping that commitment is an accomplishment. Not only does sticking to a new healthy habit make you feel more confident, but you can also spot physical improvements to your body and health over the long term.

Try things that make you uncomfortable

Stepping outside your comfort zone is, as you might expect, uncomfortable. Mr. Houpert said that’s the point.

“Confidence is ultimately about being comfortable in a wide variety of situations that would make most people feel uncomfortable,” he said. “So if you stretch your comfort zone every day, very quickly you’ll have a large comfort zone and be able to feel more comfortable even when outside of it.”

This can involve more daunting changes, like taking a new job or confronting someone you usually avoid. However, it can also take smaller forms, like striking up a conversation with someone new if you’re normally shy, or trying a new food. According to Mr. Houpert, it’s more important that you regularly expand your comfort zone rather than occasionally throwing yourself into the deep end.

Try a new look

How you dress can affect how other people perceive you, but it can also affect how you perceive yourself. Wearing different clothes can prompt you to think or behave differently. This effect isn’t just limited to feeling good about yourself. Dr. Adam D. Galinsky, a professor at the Kellogg School of Management at Northwestern University, found that participants in a study who wore a white lab coat exhibited more focused attention. In other words, when people dressed like a doctor, they behaved more like a doctor, or at least how they thought a doctor might behave. If you want to feel more confident, dress the way a confident version of yourself would.

Defy your impostor syndrome

Impostor syndrome is a nasty mental bug that convinces you that your accomplishments don’t really count and that you’re going to be found out as a fraud. This doubt can creep in because it’s easier to remember faults but more difficult to remember successes. Make a habit of periodically writing down or reflecting on times you’ve done things well. It’s easier to be confident in your abilities when you remember them.

Adjust your posture

Much like how you dress, the posture you adopt can affect how you feel about yourself. While it might feel a little silly at first (remember that tip about stepping outside your comfort zone), trying out powerful stances can help adjust your frame of mind. Research from Ohio State University suggests that something as simple sitting up straight can make you feel more confident in what you’re doing.

Avoid the arrogance trap

As you start to express yourself more confidently, it’s natural to worry about becoming arrogant in the process. However, according to Mr. Houpert, arrogance isn’t confidence run amok.

“Arrogance is more the result of insecurity than high self-confidence,” he said. “Confidence is self-satisfied while arrogance requires external validation to feel good. So you get people who brag to solicit the recognition of others. Someone with true self-confidence is capable of being assertive and standing up for themselves, but they’re unlikely to adopt a tone that others perceive as arrogant. Oddly enough, the best defense against arrogance is developing true self-confidence.”

If you start out doubting yourself, it will take time before you feel like you belong. In the interim, your own creeping doubt can try to tell you that feeling good about yourself or standing your ground is really arrogance. Recognizing that this is a symptom of insecurity — and that being aware of the symptom is its own form of inoculation against it — can help you push past it.