Double Standards

Why is it that all of us have double standards? Why is it okay for ourselves to do something illegal but then we condemn other people who may have done the same thing?

For instance, a person may love to watch chick flicks and you regard the person as lack of substance but then it's okay when you watch chick flicks yourself (FYI, watching chick flicks are just for entertainment, if you want substance, go read encyclopedias or something).

Or say for example: some tales that I heard from my friends are that their boyfriends do not allow them to dress sexily or too revealing for the fear that other guys will check them out. But it's acceptable when the boyfriends themselves check out other girls who dressed sexily.

And the most controversial example which has been debated since the 21st century is: Why do they labelled women who have multiple sex partners as sluts while they defended men who have done the same as nothing more than just a form of polygamy???

So what is the reason for these double standards?

I think I might know why.. It's because we are all selfish human beings, who only care about ourselves and those who are dear to our hearts.

p.s. I'm not saying that I'm a saint here. I do too have my own double standards, just in case you are wondering.