"Being" means "you are." If you're "being positive" it means you're always positive.
Sometimes horrible things happen. Sometimes tragic things happen. Sometimes abominable things happen.
We've learned that you can't always be positive. Some realities just aren't bursting with positivity. Some outcomes just don't have "positive" endings. You can't always be positive.
Positivity isn't a switch you can turn on. You can't just - poof - turn something horrible, tragic, or abominable into a positive. That's not real. It doesn't feel authentic. It feels fake after a while (especially when you hear other people tell you that your negative is actually a positive).
Despite the negative, I think you can make an effort to focus on other positives in your life. But I think it's important to acknowledge the negative instead of denying its existence. I think that's an essential step one needs to take in order to come to peace with the negative's existence.
You can acknowledge what's bad, but you don't have to let it consume you. You don't have to let the negative overshadow all of the positive. But you have to work at it. It's an approach that – I think – has more positive results than negative ones, and that makes it an approach worth working at.