Self-perception

I use to scoff at all the focus on posture and sitting up straight... but now after years of flexibility training I have begun to notice the mind-body connection is not a one-way street. That your mind subconsciously uses sensations and positions of your body to influence what you perceive, feel and think

The human mind is a finicky, irrational thing. It has been shown that your are kind of bad are judging yourself and so sometimes you use your actions to judge your own character. Scientists have given people counterfeit bags and found that this influences their own self-perception and so they tend to cheat more.

http://blogs.scientificamerican.com/streams-of-consciousness/why-wearing-fakes-makes-us-cheat-more-excerpt/

Similarly, I have begun to believe that if you slouch and hunch your shoulders and back - you will unconsciously start to feel "slightly" more shy and cautious... but if you sit/stand up straight and walk like you have nothing to fear... you mind will unconsciously begun to take cues from your body on how to feel. Sometimes there can lead to funny results, where if you do something to heart beating quickly (like running around or crossing a cliff) ... and then meet someone, you will unconsciously find that person more attractive because your brain mistakes the increase heart rate and alertness are because of the person and not because you just ran around a lot

https://en.wikipedia.org/wiki/Misattribution_of_arousal
http://www.spring.org.uk/2012/04/what-the-love-bridge-tells-us-about-how-thoughts-and-emotions-interact.php

So I'm not advocating pretending to be something that you are not or "fake it until you make it". But that posture and body position matter... so before you want to do something challenging... try holding a victory pose with your arms outstretched. When walking... keep decent posture and stride as if you are carefree and light-hearted if you can...