Of course. Yeah, we have no way of knowing anything outside of our own individual existence, when it comes right down to it.

But, though I don't have ironclad certainty that you actually exist and are having an experience like mine from your perspective, the decent thing to do in the absence of certainty is to treat you as though you are. And that distinction is not merely philosophical. To behave otherwise makes you a psychopath. I'm just saying until we know more, it'd probably be wise to tread lightly and behave as though they are capable of experience in a way similar to what we are.