It's partly inevitable. As others have stated, each one of us gets our own, completely unique take at life. No two lives led can ever be exactly the same. Differences in genetics, environment, education, exposure to ideas, sense perceptions etc. Quite impossible to have the same experience as another.
Beyond this, sadly (and even I perpetrate this, not saying I am above it) we all strive to be "most correct" or to believe our views on something to be more correct than others. This also, I believe, is mainly out of our hands. From an evolutionary view on it, taking stock of ourselves as social creatures, we're likely all primed to attempt to be "alpha" within our spheres of influence. But with our ability to rationalize and empathize, and in today's day and age, we don't just go around smacking down others to establish our "alpha" status, nor do we get smacked down. So this urge reveals itself along more subtle avenues. Like always trying to be "right" in a debate, or discussion. Or thinking everyone else has it wrong, or that your opinion is the most important, etc. To the point that sometimes, even if you mostly agree with someone, you may find yourself picking apart what they say anyway and literally trying to find fault with it. I honestly see this happening all the time.