Explaining "Power corrupts; absolute power corrupts absolutely"

What does it mean?

The phrase means that when a person gains power, they are likely to become corrupt or make unethical decisions. The more power they have, the more likely they are to be corrupted or act without moral restraint.

Tone

Origin

The phrase is often attributed to Lord Acton, a British historian, who wrote in a letter to Bishop Mandell Creighton in 1887, "Power tends to corrupt, and absolute power corrupts absolutely. Great men are almost always bad men."