WHY ?

Why we, as a human have the same habit each time ? We use to care what other thing of. When you wanted to buy a thing, you really love it, is the type you want, but your friend, people arround you, telling you that wasn't nice, the negative side of that thing, is not worth and so on . After that, you tend to think alot. You are in a dilemma. You want to buy it but people around you giving you a bad feedback about the thing you love so much. How ? How ? How? That only playing in your mind. Human tend to be like this . Just do not know why .
Why why tell me why ?