Why do we laugh at other's misfortunes?

I was watching one of those infamous commercials where the old lady falls down and says “Help, I’ve fallen and I can’t get up!” and couldn’t help but laugh.

so, this got me thinking. Why is it so funny when other people get hurt or someting bad happens to them? Why are we so addicted to watching fail videos online?

Do you often laugh at other’s misfurtunes? What is in us that causes this? Or am I just going to Hell?