
“If you think you can, you can. If you think you can't, you're right.”
Variant: If you think you can, you can. And if you think you can not, you are right.
“If you think you can, you can. If you think you can't, you're right.”
Variant: If you think you can, you can. And if you think you can not, you are right.
“Whether you think you can, or you think you can't — you're right.”
"On Monsieur Coué", Epigram in The Week-end Book (1928), p. 217.
Source: Born to Run: A Hidden Tribe, Superathletes, and the Greatest Race the World Has Never Seen
Can't Not
Supposed Former Infatuation Junkie (1998)