I feel compelled to point out the irony of that statment. If that statment is true, then each man is an island, seperated from everyone else and that truth is relative. However what is wrong with this? If truth is relative then the statment can be true for someone while false to another. Which means that your statment can be null to me, because I've decided that is it false. Lets take this farther. If truth is relative, each man must decided for himself what is true, and that you cannot 'force' your opinions on another. Why are you trying to convince me of it? And even farther. If thruth is relative, why should I trust what you're saying is true, when truth itself is relative?
But each man
is an island, seperate from everyone else

We cannot share experience or feelings, not from a base level, you cannot truly know how your comments or thoughts make another person feel. I am not trying to convert people, stating your own opinion is not an easy thing to do, as is not getting up tight when peoples reasons don't agree with yours (not
yours but a hypothetical reader), that's why that path is so difficult, because it's so tempting to take the easy path. But I wouldn't try to force you to become what you are not, but you can force you not to hurt anyone else by doing it. That is the challenge.
We are not things because we can choose not to be, we are the only creatures even capable of the feeling of empathy, of at least to a tiny degree being able to place our emotions in other people and creatures. That's practically magical when you think about it. Yet we use it so so rarely.
I know my eyes are seeing reality because I believe them. They are only organs that transmit information to the brain in a manner your 'self' can interpret. If you start saying your eyes are lying to you, then you will probably just keep walking into lamposts

And yes, I was referring to Christian conversion by torture as practised in less civilised days. But smaller, and larger crimes take place in all religions, even today.
I wouldn't say I trust everything, but I know what I believe, and you don't have to believe the same, that's the whole beauty of it, we've disagreed on something completely fundamental in religions, and yet have not attempted to kill each other, you would not do so in real life, if someone disagreed strongly enough, you would simply give up. So why do individuals think like this, and mobs think the exact opposite? Lack of Empathy.
So why does empathy drop as the group gets larger? Strength of numbers. A conquerable 'animal' situation. A person who realises he is a single entity, even in a crowd, is far more likely to carry empthy, than one who thinks he is part of the 'pack', because the pack will find itself agreeing on the first multi-compatible emotions, ie. fear and suspicion of the new and untested, of challenges on what they believe to be unchangeable.
So once again hard choices arise, I'm not saying it is an achievable goal, mankind, by it's own self destructive nature, would never unanimously decide to make the hard choices.
It's an interesting fact that the medical term for an individual who is incapable of empathy is 'phsycopath'.