I know that I have never been so well pleased as when I could shift power from my own, on the shoulders of others; nor have I ever been able to conceive how any rational being could propose happiness to himself from the exercise of power over others.

Thomas Jefferson (1743-1826) American political philosopher, polymath, statesman, US President (1801-09)

Letter (1811-01-26) to Destutt de Tracy
    (Source)

Often just the second clause is quoted: "I have never been able to conceive how ..."