"When you gaze into the abyss, the abyss gazes into you", from Nietzsche's "Beyond Good and Evil". It can also be understood as "when you pay attention to negative things, negative things will slowly affect you."

When we have negative emotions, we will be stared at by this "abyss", which will make us lose our minds and make some wrong behaviors.

Therefore, we should not always stare at negative things, otherwise you will be affected by it and slowly become part of the negative energy. On the contrary, always focus on positive things, and you will become more and more sunny. The abyss here can also refer to negative or evil things. When you pay attention to it for too long, it will slowly change your inner thoughts.

When you look at evil, evil is like a mirror looking into your heart.