The above quotation has been attributed to Abraham Lincoln, but probably comes from the hand of Robert Ingersoll, a gifted orator, but no matter its origin, the sentiment of this proverbial wisdom rings very true. For instance, there are loads of people that speak of injustice, unfairness, and similar ilk, to which through unanticipated and unparalleled events, become persons of power, thereby placing themselves in the very position of being true to their character and often thereby falling far short. So too, there are men born into a structure which gifts to them power, to which, to those that are given great powers, great things are expected from such a responsibility and they too fall short.
Another way, though, to test this phrase, is to replace the word "power" with "wealth", and although power alongside wealth are often entwined with one another, there are in the scheme of things, many more men with enormous wealth, than those that have enormous power, and while wealth is of itself, a form of power, it isn't the same as having the power to create or destroy others at a moment's whim.
Many people with power or wealth are inclined to believe that they are fair minded, but even within their everyday activities that is belied by the very things and actions that they demonstrate. However, of far more intrigue, are those that actually are men of good character; caring, selfless, devoted, and moral, to which, something changes within them upon the receiving of power, perhaps previously dormant, but now sufficiently awakened, that quickly evolves into what appears to be a completely different man, gone power mad. It is this man, who as with a flick of the switch, turns into something that he is not, or perhaps turns into something that he has always been, that fascinates.
The fact that power can change a man, or bring out the worst elements in a man, are very good reasons why governments, personal relationships, businesses, and so forth, should always have checks and balances within them, for it is those checks and balances that help to prevent the evil that one man can do to another, or what one government can do to its people, and instead helps to ensure that the better angels of our nature are not sacrificed at the altar of greed and power.
There are a significant amount of people that enjoy a great orator or a man with a forceful and charismatic personality, to which these great personages seem to resonate within us, because often we seek sense in a senseless world, or order in a world of chaos, but alas that isn't typically what we get in reality, as power when it gets into the wrong hands affects the good sensibilities of too many men. So that, if we are too afraid to confront, or to contradict, or to question, a man that has power, because we fear the consequences of doing so, than that man has too much power in his hands to begin with.
The reason why power tests a man's character is because power has the capacity to get you things without you having to consciously worry about the consequences, but it is those consequences, that truly do reflect your character.