Not only can one man never know the depths of suffering or joy in another man's heart, but no man can know the depths of any emotional state in another's heart. I have said that I don't believe mere humans are capable of unconditional love, but what is my belief to reality? I don't really know how anyone else can love, just as they don't know how I can love. One man will give up his life with no hope of gain in this world or the next. Another man can love five women with the same intensity and passion that other men love only one. One man can love and hate at the same time. Yet another man cannot love at all, and another man knows only hate.
We feel and experience our own lives, and we build a template through which we gauge all future events. Then we take our template and judge other men by it. What pathetic little morons we are.
(Don't mistake this for a misapplication of the "judge not, lest ye be judged" principle. I'm only talking about what a man feels, not what he does. That's a whole other story.)