“A teacher affects eternity; he can never tell where his influence stops.”
This quote has no known author and is recorded as an anonymous proverb.
About this quote
Adams is talking about the reach of a teacher's influence, which he had no way of measuring and no intention of claiming credit for. It is a description of heroism that fits almost nobody's idea of one: ordinary work, repeated for years, with the effect arriving after the person who did it has gone.
Source: The Education of Henry Adams