Developing a shared understanding through communication is complex because

a. everyone interprets the world differently

b. no one understands enough words to communicate effectively

c. learning to communicate well is too difficult

d. all of the above

The answer is A: everyone interprets the world differently.

It is a fact, for millennia well understood, that everyone interprets the world according to subjective determinations. Indeed, not only is it a fact, but even a philosophical problem that has withstood many attempts at solving it. Perhaps the most solid attempt was Kant´s theory of the understanding being based on categories that are by all shared and that permit intersubjectivity. But even Kant, when faced with the problem of beauty and the sublime, had to face the limitations of his intended universal and definitive theory. Nevertheless, as Kant himself would argue, there is consensus, or at least the possibility of it, when based on objective criteria that we can all agree on. So, developing understanding through communication is a complex process but not one that is impossible to achieve.  

the answer is not