Know your enemy.
“Never hate your enemies. It affects your judgment.”
This is one of the most popular quotes from the The Godfather Part III.
So who are, or what are, your enemies? People who are opposed or hostile to you? Things that harm or weaken you? Both are your enemies for sure.
But the worst enemy of all human beings might be hate itself because it can be easily directed toward ourselves. If that happens, it not only affects our judgment but often makes us blind.