oh no my mom died but don't worry I'm not sad there's other things to enjoy in life.

As a psychotherapist, "don't be sad" is invalidating a person's emotion and can be very toxic, if used flippantly. There are plenty of reasons to be sad. Someone wouldn't feel sadness if there's no reason for it. Don't ever tell a person not to feel something. Rather, rephrasing it as "you can choose and nourish happiness," can be more therapeutic than simply saying "don't be sad."