Chandniji very nice question and respected friend Jura's answer is very nice. I am agree with her. This is totally depend on our mind and thought. If we will think always in positive way we never will be sad. Always think one thing our life is not so long, Art is long but life is short. We should make friends. We should communicate our thoughts to each other. You know kids are very happy then young, why? Because they use word forget in their life.They fight in morning and talk again in evening. This is very nice way of life. Negative thoughts always gives us negative attitude. He/she, who is polite gets everything. So try to live with positive think, positive friends, positive attitude, positive work and with nice book and keep smile always. hahaha