
“If you think you can you can, if you think you can't you're right!”
“If you think you can you can, if you think you can't you're 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.
“You can lead a horticulture, but you can't make her think.”
Parker's answer when asked to use the word horticulture during a game of Can-You-Give-Me-A-Sentence?, as quoted in You Might as well Live by John Keats (1970).
Source: You Might as Well Live: The Life and Times of Dorothy Parker
“You can think all kinds of things. But you can't know for sure.”
Source: The Hunger Angel (2012), p. 61