First, people have different ideas. Some people love Thai food, some people hate Thai food. For example, I am the one who always avoid to eat Thai food, and my dad is the one who always recommend others to eat Thai food. He is my father, I think we should have similar food taste, but actually we don't. People have different ideas on this kind of simple things, so when people are dealing with much more complicated stuff. People are going to fight for their preference all the time.
Second, people have different kinds of life styles because their family. My mother doesn't push me to sleep early, nor she doesn't plan my life for me. She doesn't care about my grades, but she cares about my violin class and sports. She always forces me to play the violin more, instead of studying in my own room. She always drags me to play some sports in the morning. I know that she won't harm me for sure, so I just copy what she tells me to do. But some people might have totally controversial family style than me.
People were raised and born differently, so how can they all be the same! I think tolerate each other is a really important thing in our life!