Why do people like or dislike stuff?

People will say they like something or don't like something all the time but if you actually take the time to ask them why they do of don't they will probably have a hard time telling you there reasoning.  Some people don't think it is important to have supporting evidence to a question like that but when you do it can really help carry on a conversation and bring more meaning to what your opinion is. I think it is important to know why or why not before coming to the conclusion or liking or not liking something. Because if someone you are talking to is not sure on there opinion you can not neccasarrily tell them what to think but help them figure out how they feel about it. I understand when someone is leaning towards one or the other but they are not sure why so they think more about it but to just come to the conclusion that you like or dislike something without knowing why makes it seem like you don't really truly know your just picking a side based off of what you may have heard someone else say or show you.