There may be nothing worse than a negative person sucking the life out of you. Especially, if they are in a leadership position. After all, one of the most important characteristics of a leader is optimism. The leader has to believe with all their heart that the mission is going to be achieved. If their is any inkling of negativity, every person that follows them becomes a car on that train to nowhere.
Research has shown that optimism is a competitive advantage. In a study conducted at Duke University by Manju Puri and David Robinson, they found that optimistic people work harder, are paid more, win at sports more often, are much more successful in getting elected to office, and live longer.
One of my favorite leaders of all time is Steve Jobs. In is book by Walter Isaacson, Steve Jobs, the author talked about Job's Reality Distortion Field. He was constantly inspiring his team to push further, to achieve almost impossible things and meeting ridiculous deadlines constantly. What Jobs did was lead his team out of thinking pessimistically, or in many cases realistically, into overbearing optimism. Because of his belief, he created one of the most successful company's ever and changed the world.
To achieve the unthinkable you can't think like everyone else. You have to believe with all certainty you can accomplish it. If everyone thinks you're crazy, you're probably on the right track.