Source, in full
Commonly quoted on the internet, this quote is actually from Karl Grossman, via his 1980 book Cover Up: What You are Not Supposed to Know About Nuclear Power (p. 155; freely available online via its publisher; see PDF page 187).
More quotes by Albert Einstein
A happy man is too satisfied with the present to dwell too much on the future.
Try to become not a man of success, but try rather to become a man of value.
Life is like riding a bicycle. To keep your balance you must keep moving.
Attribution
Quote text and notes from Wikiquote: Albert Einstein (page history), available under CC BY-SA 4.0. Source quality and labels are our own summary of what Wikiquote records.