Confidence is generally described as a state of being certain either that a hypothesis or prediction is correct or that a chosen course of action is the best or most effective. Self-confidence is having confidence in oneself. Arrogance or hubris in this comparison, is having unmerited confidence - believing something or someone is capable or correct when they are not. Overconfidence or presumptuousness is excessive belief in someone (or something) succeeding, without any regard for failure. Confidence can be a self-fulfilling prophecy as those without it may fail or not try because they lack it and those with it may succeed because they have it rather than because of an innate ability.

8 Scientifically-Backed Ways To Feel More Confident Even When You're Not   - Huffington Post - September 2, 2014

Confidence: Highly coveted, yet often elusive. We dedicate time and energy to cultivating the feeling so we can tap into it when we need it most: at work, in business meetings, on dates, during tough conversations. Fortunately, there are a few science-backed tricks to get us there (even when we totally don't feel it). If you're feeling less-than-stellar, these simple, actionable tips will help you fake it 'til you make it:

For starters, stand tall.

Tall, correct posture is the hallmark outer sign of confidence - and research shows standing up straight will help you feel it on the inside, too. A study published in the journal Psychological Science showed that a tall, expansive posture helps you act and feel more powerful than more drawn-in stances. Your posture can also increase confidence-boosting testosterone in the body and be a potential indicator of success.

Dig out that old rap album.
Getting ready to request a raise or ask someone out on a date? Just press "play." Researchers found that listening to bass-heavy tunes may have the power to make you feel more confident.

Recall a time you were powerful.

Making everyone laugh in your best man speech, nailing that job interview, publishing a well-written piece -- whatever it is, those small moments of confidence can make an impact when you're not feeling your best. Channeling a moment when you were genuinely captivating can make you feel (and as a result, act) more confidently. Reviewing your credentials and accomplishments by looking at your resume also may do the trick.

Indulge in your morning ritual.
Those first few seconds when you put yourself together in the morning aren't just crucial for starting your day -- they can bring a surge of self-confidence, too. And while the whole concept may seem more vain than valuable, there's still something to be said for that grooming ritual if you turn it into a mindfulness opportunity find the simple way to do it here. More confidence and calming thought awareness? We'll take it.

In that same vein, choose your outfits wisely.

Chances are you've heard the old adage to "dress for success" -- and there's a reason these cliches have longevity. Studies suggest that what you're wearing can have a direct effect on how secure and powerful you feel. Researchers found in an experiment that those who wore white doctor coats (in other words, a piece of clothing associated with a certain quality -- in this case, care and intelligence) performed better on the experiment's administered test than those who did not.

Brush up on your Spanish.
Learning a new language or sharpening other cognitive skills can boost your life satisfaction in a similar way to a pay raise.

Stretch those muscles.

Sometimes all it takes is a good, lengthening stretch to feel like your happiest self. Stretching your muscles can lead to good posture, better blood flow and ultimately more confidence. Certain stretches can help calm you down.

Channel your favorite celeb.
Often we think of Hollywood stars like George Clooney, Lupita Nyong'o and Jennifer Lawrence as people who make us feel inadequate, but this exercise can actually help do the opposite. A study published in the journal Personal Relationships found that when people with waning self-esteem wrote down positive qualities they see in their favorite same-sex celebrities and themselves, they felt much more compelled to become their best self.