My husband and I are opposite on a lot of things....like the way we deal with stress. I bring him back down when he freaks out about finances. He kicks me into action when I have to finish different things. When 2 people are too much alike, it's like dealing with a mirror image of yourself. You like to look at it for a while, but eventually it gets boring and you want more.
That being said, there needs to be a lot that you have in common. It's very helpful if you like the same kind of books, if you have the same kind of thoughts about some controversial issues, if you like the same kind of video games. But it's good to have new ideas introduced to you because your partner has different views on things. That's what helps bring you together as a couple and helps diversify yourself.
They do not always think alike, they do have some disagreements every once in a while. If they were always thinking the same thing, that would be boring.