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Note: This utterance is often incorrectly attributed to Dr. Seuss.
The quote said to be from Dr. Seuss is actually widely circulated misattribution. “Those who mind don’t matter, and those who matter don’t mind” actually came from FDR presidential advisor Bernard Baruch, about his dinner party seating arrangements.
According to Wikiquote:
Bernard Mannes Baruch (19 August 1870 – 20 June 1965) was an American financier, stock market speculator, statesman, and presidential advisor. After his success in business, he devoted his time toward advising Democratic presidents Woodrow Wilson and Franklin D. Roosevelt on economic matters.
["Those who matter don't mind, and those who mind don't matter" was Baruch's] often-quoted response to Igor Cassini, a popular society columnist for the New York Journal American, when asked how he handled the seating arrangements for all those who attended his dinner parties, as quoted in Shake Well Before Using: A New Collection of Impressions and Anecdotes Mostly Humorous (1948) by Bennett Cerf, p. 249; the full response was “I never bother about that. Those who matter don’t mind, and those who mind don’t matter.” This anecdote … has also become part of a larger expression, which has been commonly [and incorrectly] attributed to Dr. Seuss, even in print, but without citation of a specific work : “Be who you are and say what you feel, because those who mind don’t matter and those who matter don’t mind.”