Our Passions, Ambition, Avarice, Love, Resentment &c possess so much metaphysical Subtilty and so much overpowering Eloquence, that they insinuate themselves into the Understanding and the Conscience and convert both to their Party. And I may be deceived as much as any of them, when I Say, that Power must never be trusted without a Check.

John Adams (1735–1826) American lawyer, Founding Father, statesman, US President (1797–1801)

Letter (1816-02-02) to Thomas Jefferson
    (Source)