Yes, because we are selfish. Don’t be shocked even if you think you are not and you think that you also love others and are willing to give and care so much. YOU ARE STILL SELFISH (and it's all about your happiness).

People are divided into two groups;

Group one (It's all about me, myself and I):
You always want to be happy by doing things that satisfy your instincts, by letting people do whatever please you, and by blaming the world all the time for not appreciating your existence.

Group two (Mr. and Mrs. IF'S):
You always blame yourself for not having had chances, for not choosing the right course of action, for not loving enough and you always relate your satisfactions and happiness to other people's satisfaction and happiness. Now you are going to ask yourself how I can be selfish when I do that. Draw a triangle and write at the bottom of one corner “ME”, and the other corner “OTHERS” and at the top corner (HAPPINESS), then make an arrow regardless of any direction you want either clockwise direction or the opposite direction.

If you are seeking happiness from others IT'S THROUGH YOU, if they're seeking happiness from you IT'S THROUGH THEM, if you or they seeking happiness IT'S RELATED TO BOTH OF YOU. So whatever the foundation is... the goal is your happiness to make others happy, or THEIR HAPPINESS THAT MAKES YOU HAPPY?

So it's all about you. Even mother Theresa is another happy person who shared her happiness with the rest of the world.