oblivious

you can never really tell what someone is thinking. even your best friend, or significant other, or twin sister. you can never really put yourself in his or her situation and state of mind such that you can comprehend every single thing that is going on in that person's life and come up with the same thought processes. not to mention the prior experiences and conditionings that result in one's logic (or lack thereof). the point is, you can never really come to the same conclusions and objectifications that you may think you do when you say 'yeah man, i totally get what you mean'.

now, this is not to say that you can never have the same ideals or philosophies or ideas as that person, just that it can never (or at least very very unlikely) be the same as the other's. but this does not entirely matter in the bulk of situations, because as long as you're in the same ballpark, you've every right to say that you can empathise, or relate, or even propose any further constructions upon the idea.

it does matter, however, when you are considering something that a person considers entirely personal, maybe even a novel feeling that to many of us, when we encounter it, the ephemeral feeling is that of something nobody else in the world has ever or ever will reproduce. and in these situations, sometimes it is counterproductive to say that 'yeah man, i totally get that'. instead, you might be more expected to just remain silent and nod.