“The young man knows the rules, but the old man knows the exceptions.”
Attributed in the Sioux City Journal http://www.siouxcityjournal.com/ (6 Jul 2008), p. A8
In fact, from a " Valedictory Address https://books.google.com/books?id=7joCAAAAYAAJ&pg=PA426&dq=The+young+man+knows+the+rules,+but+the+old+man+knows+the+exceptions&hl=en&sa=X&ved=0CCcQ6AEwAmoVChMI1-e4oOewyAIVWFmICh0eVQsI#v=onepage&q=%22The%20young%20man%20knows%20the%20rules%2C%20but%20the%20old%20man%20knows%20the%20exceptions%22&f=false, delivered to the Graduating Class of the Bellevue Hospital College" in 1871 by Oliver Wendell Holmes, Sr, reprinted in the New York Medical Journal 13 (April 1871): 426.
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Oliver Wendell Holmes Jr. 107
United States Supreme Court justice 1841–1935Related quotes

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Context: People expect old men to die,
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