The moment a man, or a class of men, find themselves with power in their hands, the man's individual interest, or the class's separate interest, acquires an entirely new degree of importance in their eyes.
 John Stuart Mill, Considerations on Representative Government (1861). copy citation

Context

“Now it is a universally observed fact that the two evil dispositions in question, the disposition to prefer a man's selfish interests to those which he shares with other people, and his immediate and direct interests to those which are indirect and remote, are characteristics most especially called forth and fostered by the possession of power. The moment a man, or a class of men, find themselves with power in their hands, the man's individual interest, or the class's separate interest, acquires an entirely new degree of importance in their eyes. Finding themselves worshipped by others, they become worshippers of themselves, and think themselves entitled to be counted at a hundred times the value of other people, while the facility they acquire of doing as they like without regard to consequences insensibly weakens the habits which make men look forward even to such consequences as affect themselves.” source