My therapist said that happiness comes from within. Somewhere, deep inside you, there is a core you that is able to observe your thoughts and emotions without judgement- the you that contains your inner wisdom and strength. When you tell yourself that you feel sad, or that you're a failure, or any other number of negative thoughts, your brain is going to listen to that and respond accordingly. But your core will always be there, observing. Your core can decide whether you start thinking positively about yourself (I know- it's hard!). Your body will thank you for it.