Karma is the idea that what goes around comes around. You do a bad deed, the universe will deliver its judgement on such behavior.
For the more science-minded (rather than religious-minded) among you, this is cause and effect in action. Either way, the result is the same.
This video shows instant karma being meted out time and time again. Watching this makes it hard to imagine such a thing as karma doesn’t exist, because this could easily be considered as evidence.
We see idiot drivers mindlessly overtaking and hitting barriers, acts of violence towards others which end up with the perpetrator being hurt, and selfishness rewarded with just desserts.
