Reasoning will never make a Man correct an ill Opinion, which by Reasoning he never acquired.

Jonathan Swift (1667-1745) English writer and churchman

Essay (1720-01-09), “Letter to a Young Clergyman”
    (Source)

Earliest version of this general sentiment, which has been attributed to (or at times borrowed by) figures such as Mark Twain, Sydney Smith, Fisher Ames, and Lyman Beecher.

Variants:

• Reasoning will never make a man correct an opinion that they have not reasoned themselves into.
• Men are not to be reasoned out of an opinion that they have not reasoned themselves into.
• Reasoning will never make a man correct an opinion, which by reasoning he never acquired.
• It is useless to attempt to reason a man out of a thing he never was reasoned into.
• We may never reason a man out of an opinion which he was never reasoned into.
• You cannot reason a man out of what he never reasoned himself into.
• You can’t reason someone out of something they weren’t reasoned into.
• He cannot be reasoned out of error, if he was not at first reasoned into it.
• What has not been reasoned in, cannot be reasoned out.
• Never try to reason the prejudice out of a man. It was never reasoned into him and it never can be reasoned out of him.
• It is useless to attempt to reason a man out of anything he was never reasoned into.

For more information about this quotation: You Cannot Reason People Out of Something They Were Not Reasoned Into – Quote Investigator.