People with positive attitude ... in the literal sense ... are easy to spot because they're being, feeling, and doing things for themselves.
Even just sitting around, positive people bring this attitude "I'm right where I want to be." or "I'm looking forward to something good."
But they don't sit around that much. They're doing things. Moving. Smiling. Working. Learning. Making friends. Beating records. Starting projects. Enjoying themselves. Making a difference.
The one thing 'positive people' don't do, IMHO, is wait for someone else to make a move. "That'll never fly." "Not In My Back Yard!" "Yeah, well, I could do better but I haven't got around to it."
People who react negatively can be useful, and even make a positive difference (fighting evil and all that), but they are not as powerful as positive people.
Positive people make things happen; when blocked, they adapt quickly and keep moving forward.
Negative people wait for someone else to move before they react. They are stopped by their fears: of disappointment, of change, of hurt.
We're all positive people sometimes; do you know anyone who lived an entire lifetime without happiness or hope?
We all go negative sometimes too. Grief, denial, loss, and fear are part of life, and the only way out is through.
It pays to listen to fear, and let it guide you around danger. But it pays even more to listen to hopes, and put a smile on your face every morning.