Confidence
That is right, if you are someone who lacks confidence and is in need of a quick boost, there is an answer for you. It is called improving your posture and basically lying to yourself that you are a lot more confident than you actually are. Just by improving your posture, you can trick your brain as well.
By standing up straight while you sit, or maintaining good posture when you walk with your head up and chest out, you subconsciously feel more confident. If you manage to maintain this, you can over time become confident in yourself and others will believe in you more when they notice how strong and capable you look.