If you make decisions quickly, you are someone who is decisive. A decisive event can settle something, like a war.
People who are wishy-washy are the opposite of decisive: being decisive means you don't waffle or take forever to make up your mind, and then you stick by what you decided. People admire politicians, coaches, and friends who are decisive. In sports, if a home run won the game, that was the decisive run. When you reach a crisis point in life — when things are going to change one way or the other — you've reached a decisive moment.