When faced with a negative situation, many of us want to correct the problem. We often think to look on the upside and share that with others. Our attempt to shift a negative emotion to a positive one seems like a good idea, but it actually makes things worse.
Peter Bregman, writing for Psychology Today, explains why:
Countering someone's negativity with your positivity doesn't work because it's argumentative. People don't like to be emotionally contradicted and if you try to convince them that they shouldn't feel something, they'll only feel it more stubbornly. And if you're a leader trying to be positive, it comes off even worse because you'll appear out of touch and aloof to the reality that people are experiencing.
He also suggests a better approach. Instead of telling the negative person to look on the bright side, validate how they feel and agree with them when you honestly can. Finally, find out what they are positive about and encourage it. You can't force your specific positivity on others. It makes the problem worse. Instead, look for their positivity and help it grow.
How to Respond to Negativity [Psychology Today]