"Power tends to corrupt, and absolute power corrupts absolutely. Great men are almost always bad men."
This is a theme of much literature and a daily meme on the news. We see this and in our hearts know there is some harmony with the idea.
Don’t let it poison your thinking. I don’t know the full context of Acton’s remarks but they were made in a letter to a bishop so spiritual issues may have been under discussion. To Christians this is based on our belief in the carnal nature. Men are born with a sinful nature. If we stop there all is despair. But we don’t stop there. We go on to grace and the power of the Holy Spirit. Without God’s touch the statement is totally true but with God’s touch our character can be transformed.