Try to look at the bigger picture

What else is in your life that makes it worth living? Try to think about all of the other things that you value in life, such as your friends, family, and health, and youll see that you probably have much to be happy about and thankful for, even if you dont feel very happy or thankful in the moment. Numerous studies have shown that gratitude is deeply connected with happiness.
Think about good memories. If youve lived through them once, you can have them again. Thats the beautiful thing about memories just because things may seem bad right now doesnt mean that theyll be that way tomorrow.
In the case of sadness based on a minor life event, such as getting a bad mark on an assignment, put the event into perspective and consider whether youll feel sad in 10 years and whether the event will even matter then. Consider using that old phrase, dont sweat the small stuff.