Look at this quote by John Stuart Mill:
It is better to be a human being dissatisfied than a pig satisfied; better to be Socrates dissatisfied than a fool satisfied. And if the fool, or the pig, is of a different opinion, it is only because they only know their own side of the question.
I have a problem with finding out the meaning of the sentence after because, that is they only know their own side of the question. I know the meaning of each word but I am not sure what it means. How would you paraphrase it?