When we empathize with another, we feel what they feel. We understand their situation and can relate to their problems. We remember situations where we encountered difficulties similar to what the other is experiencing. Empathizing with them, their suffering becomes ours.
Isn't this a good thing? The way a caring person reacts to the suffering of another?
If we don't handle the suffering correctly, no.
When the Buddha encountered Angulimala, a serial killer, the Buddha understood and knew the terrible suffering that Angulimala was undergoing. The Buddha also understood and knew the suffering of all the past victims and of their loved ones. If the Buddha had taken in all that suffering—like a sponge—it would have tainted his calm, clear mind.
Instead, the Buddha saw everything perfectly—like a mirror. Seeing everything perfectly, his mind retained its clarity. And in an instant, he knew the right words to say to enable Angulimala to wake up from his nightmare and to turn away from killing.
As ordinary beings, when we act from empathy, our mind acts like a sponge, absorbing all the pain, anger, and fear that is overwhelming the other person. We are like a compassionate person who jumps into a raging river to save a drowning man.
Too late we realize that, never having learned how to swim, now we too are drowning.
The alternative?
View the suffering of the other as if in a mirror. See everything clearly. Then react calmly. And if there is a way, we will be much better able to discern it and help the other person.
So we have a choice as to how to react to the suffering around us.
We can absorb it and like a sponge become increasingly soiled with time.
Or we can see it clearly and remain pure while we truly help others.