Who decide it?

Most people have their own decision, and they believe that whatever they decide, it is their own decision. I also believe that when I do something, I need to make sure and decide something, and it is my own decision. However, Dan Ariely, who is Economist in MIT and speaker, said that sometimes, our determination is changed by other things. When we choose or decide something, it is confused what we should choose. For example, when we buy something on the internet or sign up for a membership, there are several different type of plans, but one is very week, the other one is very unfair, and the last one is just fair, but expensive. By this I mean that kind of that marketing makes us changing our decision. We often need to decide something as soon as possible, but In my opinion, Before deciding, thinking about it one more.