“The measure of a man is what he does with power.”Plutarh · Moralia · 100 · Moralia, Cum să te lauzi fără să te faci rău (De se ipsum citra invidiam laudando), 543D
Power doesn't change character, it only removes its mask.
Power works like an X-ray of character: it removes the fear of consequences that otherwise keeps behavior in check. A subordinate can be polite out of caution; someone who rises high and stays decent does so from conviction. The mechanism is simple: when power frees a person from any penalty, the only thing still governing their choices is what they carry inside. A manager who, after the promotion, still remembers everyone's name and still takes criticism says more about himself than any speech could.
The card says the real test comes after someone gets power. But you can predict the result earlier. Watch how they treat people who can do nothing for them: the receptionist, the waiter, a colleague from another department. Someone rude to the powerless is already showing their character; fear of the boss only partly hides it. A candidate charming to the director but sharp with the assistant will most likely be a different person after promotion. So don't wait for the test: look for its miniature version in everyday encounters. The next step is what you do once you notice these signals.
Why it matters It helps you size people up before handing them responsibility: in hiring, promotions, or deciding whom to back. The real test comes after they get the power.