Sometimes people just need to hear that it's ok. It's ok to make a mistake. It's ok if you're not perfect. It's ok to miss someone. It's ok to cry. It's ok to be different. <---- I'm doing most of those things right now. Thank you, random citizen.
They forgot play an instrument. Go for a run or a bike ride. Read or write poetry. Listen to classical music. But most of all...do something for someone else, someone who has less or needs more. The ultimate two cures for sadness are time and perspective.