"The mind that opens to a new idea never returns to its original size."

Misattributed

Commonly attributed to Albert Einstein, but this phrasing traces to Oliver Wendell Holmes Sr., who wrote in The Autocrat of the Breakfast-Table (The Atlantic, September 1858): 'Every now and then a man's mind is stretched by a new idea or sensation, and never shrinks back to its former dimensions.' The Einstein attribution first appears on Usenet in 1998, 140 years later, with no supporting source.

Actually said by: Oliver Wendell Holmes Sr.

Source