The hardest thing in the world to understand is the income tax.
In 1963 a letter written by Leo Mattersdorf appeared in Time magazine with the following assertion: “From the time Professor Einstein came to this country until his death, I prepared his income tax returns and advised him on his tax problems.”
Mattersdorf then told the following anecdote about Einstein:
One year while I was at his Princeton home preparing his return, Mrs. Einstein, who was then still living, asked me to stay for lunch. During the course of the meal, the professor turned to me and with his inimitable chuckle said: “The hardest thing in the world to understand is income taxes.” I replied: “There is one thing more difficult, and that is your theory of relativity.” “Oh, no,” he replied, ”that is easy.” To which Mrs. Einstein commented, “Yes, for you.”
1963 February 22, Time, “Letters: Feb. 22, 1963″, Time, Inc., New York.
(Online Time magazine archive; Accessed 14 FEB 2013)