It is best not to notice or try to analyse and understand the perverse side of others. Doing so implies that there is something akin to that in our own nature. And even if it is not there then by thinking about the defects of others we tend to get identified with the very same defects.
As to the cause it is due to a selfish joy that people feel when others are in difficulty. It makes them feel happy because they are not caught in a similar situation. Of course sometimes it is due to jealousies as well but most often it is the selfish sense of relief that one is not in the difficult spot that the other person is.
Affectionately,
Alok Da
