[c-linkage]

We focus on negative outcomes because that relates directly to survival. Our brains are wired for it. Talking about negative outcomes means we learn about them and have a better chance of avoiding them. Plus, the fear response is much stronger and lasts longer than the happy / joy response.

Note that for humans and other social animals "survival" doesn't always mean life or death -- it can mean being included or excluded from a social group which indirectly affects survival chances.