He who learns but does not think is lost. He who thinks but does not learn is in great danger.

Eleanor Roosevelt (1884–1962) First Lady of the US (1933–1945), politician, diplomat, activist

(Misattributed)

This quote is often attributed to Eleanor Roosevelt, and, where a source is given, usually to her Autobiography (e.g.). I am unable to find it in that work, nor in the three earlier separate memoirs she wrote, nor in any other written source.

If she did use the phrase, she was quoting from the popular Waley (1938) translation of Confucius, Analects, 2.15.