Inhale confidence, exhale doubt Accept you for you, and let your strength and passion be bigger than your fears

This phrase is literal in origin, in John 20:24-29 Thomas and Jesus had an exchange that earned Thomas the label "doubter." Then the nickname or label used for other people first appeared in 1883. The meaning then is still the meaning today of the term. It is used to describe someone who is a habitually doubtful person, in other words a person who refuses to believe anything until they are given proof. ( source )