Even though there have been a few kinds of research stating that opposites do not attract and that people tend to fall for those with whom they share similarities, it's still a question of preferences. Some folks feel more comfortable spending their time with people that have a similar lifestyle or share a mutual interest – others find it exciting when their significant other is a complete contrast to their personality.
Either way, it's impossible to have a totally identical mindset to your partner, which is why every relationship is prone to surprises. Though, of course, sometimes being different than your lover is way more fun.