A couple days ago, I was talking with one of my friends. At one point, she called me decisive. I thought about it for a while, and told her that I didn't agree with her. I only appear to be decisive.
A decisive person is quick to decision. When given a situation, they immediately make a decision and that's the thing that's done. And if it doesn't work, you friggin' make it work. That's not me at all. The only reason I might look decisive is that I don't share my opinions until I am sure of them. If I am flip-flopping between what I think my be right or true, I am keeping my thoughts to myself. The only reason I would look sure of my ideas is that I have carefully measured every possibility and chosen the best option.
My friend said that my belief was inaccurate. In fact, it was the qualities I described that proved me to be decisive. I let the conversation go, but I kept thinking about it. I finally got around to looking up the word and found that we were both right.
Decisive people may be very bullheaded and shoot from the hips. They may also be very methodical and fully-thought-out planners. Just depends on which definition you choose.
Our language is frustrating like that. It's bad enough that any given word connotes several possible meanings, but the denotations themselves can vary wildly in a given word. How on earth are we supposed to be able to communicate when our tools of communication are about as rigid as jello?