Negativity is something that most people say they don't like. Negativity is also incredibly common. Why?
Well, being negative is easy. Being negative means that you simply say no to what everyone else is working towards and proposing without adding anything to the equation. Being negative and focusing on the fearful is the quickest way to place yourself in the limelight without actually having substance behind your voice.
Everyone wants to sound like the smartest person in the room, from politicians running for the Presidency to your coworker whose gunning for that promotion. Behaving negatively means that one can sound smart and cautious when other ask people to look to the future and build. This is incredibly common in group settings and it's something a true leader and forward thinker avoids.
Where others focus on the downside, it's your job to build the upside and create positive alternatives and futures to whatever dilemma you and your comrades are facing.
If you're working on a project and a team member seems to only ever list catastrophic problems that could potentially maybe one day possibly happen, take a step back before getting annoyed. Remember that this team member might have a few good, constructive points hidden in the negativity and you can find them by asking probing questions. Pull away the hysteria by asking them to quanitfy and specify their predictions of doom. Soon you'll find that what was impossible a few moments earlier was actually a comment on a weaker aspect of the project you're building together.
Doom and gloom is easy, constructive criticism and vision are hard. Be your best self and lead your colleagues away from negative excuses to positive events.