Two people sit opposed to each other. In between them is a cup:
One person argues: the handle is on the left. The other argues: the handle is on the right. Even when talking about a cup there can be disagreement.
Disagreement often rises from different points of view. Only when two people share the same point of view we could establish if one of them is wrong.
If two people disagree, there are three possibilities:
- One of them is right and one of them is wrong.
- They are both right.
- They are both wrong.
If they are disagreeing over a matter of empirical fact, then #1 or #3 might be true. (As a trivial example, if one person says the capital of New York State is New York City, and another person says no, it’s Poughkeepsie, they’re both wrong–the capital of New York State is Albany.) My own observation is that many times, on a wide variety of subjects, #3 is the safe bet.