"I think that it's important to really question this knee-jerk reaction that we are our own best experts," said Professor Simine Vazire of Washington University.

"Personality is not who you think you are, it's who you are."

"Some people think by definition that we are the experts on our personality because we get to write the story, but personality is not the story -- it's the reality."

"So, you do get to write your own story about how you think you are, and what you tell people about yourself, but there still is reality out there, and, guess what?"

"Other people are going to see the reality, regardless of what story you believe."

Evidence of personality traits are obvious in the choices we make -- the clothes we choose to wear, how we decorate a bedroom, the content posted on a social networking site, and so on.

"Everything you touch you leave a mark of your personality," Professor Vazire said.

"You leave traces unintentionally."

"You give off hints of your personality that you don't even see yourself."

She used a battery of tests on 165 volunteers and discovered that while people were good at assessing their own internal traits such as anxiety, other people were better at observing external traits such as extroversion.

“You probably know pretty well your anxiety level, whereas others might not be in the position to judge that because, after all, you can mask your inner feelings,” said Professor Vazire.

“Others, though, are often better than the self in things that deal with overt behaviour.”

Professor Vazire believes that desirable traits such as intelligence, attractiveness, and creativity are hard for the self to judge objectively.

"There is so much at stake, meaning your life is going to be so much different if you are intelligent or not intelligent, attractive or not," she said.

"Everybody wants to be seen as intelligent and attractive, but these desirable traits we’re not going to judge accurately in ourselves."

We are better at judging friends’ intelligence than our own 'because it’s not that threatening to us to admit that our friends aren’t brilliant, but it’s more threatening to admit to ourselves that we’re not brilliant.'

A classic example of this is how we perceive ourselves in the mirror.

"We look in the mirror all the time, yet that's not the same as looking at a photo of someone else," Professor Vazire said.

"If we spent as much time looking at photos of others as we do ourselves, we'd form a much more confident and clear impression of the other's attractiveness than we would have of our own."

"Yet after looking in the mirror for five minutes we're still left wondering, 'Am I attractive or not?'"

"And still have no clue.'

"And it's not the case that we all assume that we're beautiful, right?"

For some personality traits, she says we miss the point if we look at thoughts and feelings and ignore the behaviour.

Bullies, for example, have thoughts and feelings that tell them they’re insecure and want to be liked and admired, which is not a horrible, nasty notion.

But they cannot see their behaviour as nasty and horrible, though, because their thoughts obscure their actions.

Similarly, if you think that you are warm and friendly, but friends and family say that you don't come across that way in reality, you might pay more attention to your behaviours.

"I believe I've presented evidence that should make people think twice," said Professor Vazire.

"On average, the people who know you best know you as well as you know yourself, no better, no worse than you."

'More importantly, there are things that both you know that they don't know, and things that they know that you don't know, and those lead to very interesting experiences and disagreements."