I think it’s good to be positive and optimistic. Sometimes things don’t go as planned, and sometimes bad things happen. If not taken too close to heart, negative events have less impact overall, in my experience. Obviously we’re not talking here about really sad stuff, like diseases or death. Just in general.
What I’ve noticed is that negativity is very relatable. People like to talk about their problems, and when I don’t talk about my problems in response (usually because I don’t have many and if I have some I try not to give them too much attention), I often see that people feel I don’t resonate with them.
When a person experiences sadness, being overly positive can be perceived as being dismissive. Like their problem doesn’t matter. So I don’t want to be cheering them up too much if they’re sad. Mourn with those who mourn. But I also am a poor partner in sharing sadness. The best option is always too listen, not interrupt, and let a friend talk as much as they need. I’m genuinely interested, and I’d like to come up with a solution, but I shouldn’t. Fixers are dismissive. There’s time to be sad.
If a person is too optimistic and dismissive about their problems, the problems might not get solved early enough. Prevention is better that cure. So you want to have a bit of constructive complain, and it should lead to action.