
“The hardest thing in the world to understand is income taxes.”
Attributed by his friend Leo Mattersdorf, who also said that "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." In a letter to Time magazine, 22 February 1963. See this post from The Quote Investigator http://quoteinvestigator.com/2011/03/07/einstein-income-taxes/#more-2031 for more background.
Attributed in posthumous publications