Friends are people who comes around and be there for you.
They share your burden, problems and your happiness.
They are also the people who often take you for granted.
1. You're to share their burden.
2. You're to solve their problem.
3. You hear their happiness but never activate it.
You faces more problems than usual. Your + Their problem goes back to oneself.
Then, these problems weigh you down. 
It's a double reverse cycle, realize it?