Our founders were insightful students of human nature. They feared the abuse of power because they understood that every human being has not only "better angels" in his nature, but also an innate vulnerability to temptation — especially the temptation to abuse power over others.
Our founders understood full well that a system of checks and balances is needed in our constitution because every human being lives with an internal system of checks and balances that cannot be relied upon to produce virtue if they are allowed to attain an unhealthy degree of power over their fellow citizens.

NYU Speech (2004)