According to what I've heard, servants used to whisper "Memento Mori" (Remember, you will die) to Roman leaders to keep them from becoming too obsessed with power. However, I've found little information about this online; is there any historical evidence this was actually done in classical Rome?
I recall from my Latin classes that it was a part of the ceremonial parade of the triumph. The man the triumph was dedicated to would have their face painted red to evoke the personage of Jupiter (correct me if I'm wrong) and would be treated as a living god for the day. before they entered the temple of Jupiter to pay their respects, a servant would whisper in their ear "Memento Mori" for the reasons you describe. They were being treated as divinity, so a need was present to deter them from acting that way all the time.
The most famous of these instances would probably have been Julius Caesar, as he had four triumphs at once, and thus the most reason to feel haughty.