Ultimately, we are all infinitely alone. No matter how close another person may get to us--physically, mentally, emotionally, spiritually--no one other person can ever climb inside us and muddle about in our thoughts and emotions just as we experience them, or take a walk in our shoes, to quote a cliche. In that sense, we cannot ever be fully known by another person. That's an isolating feeling, is it not? To realize that we are all truly alone within ourselves. It's an interesting concept to ponder. This idea of pure isolation. It's almost frightening.
The notion can foster and breed a multiplicity of responses. As already stated, fear is one possible reaction. However, another possible response could be that of the victim. If we cannot ever be fully known, then we must all live and function as horribly mis-understood individuals. This could sadly create a society of purely self-absorbed, egotistical human beings who care about nothing other than wallowing in the reality of "unknowablness," and thus people would cease trying to know anyone or be known themselves. Resultantly, human connections: family, friendships, marriages, etc. would cease to have meaning or value, and society would crumble beneath the weight of the unknowable self.
So, with this knowledge, will we as humanity choose to retreat even further within ourselves, or will we try all the harder to open ourselves up to those around us, in hopes of being known, if not in full, then at least in part...? What's better, to be known a little or to not be known at all? Your choice.