In Yogic philosophy, we know there is a connection between our breath and our emotions or mental state. If we breathe properly we can literally calm the mind. There are even certain breathing practises for specific purposes.
This is actually a truly empowering idea. It may be daunting but you can change your beliefs and experience your reality very differently. However, repeating an affirmation or making a vision board is not always enough. We actually truly need to believe it, feel it and most importantly our subconscious mind needs to be convinced too.