While mathematically, it might make sense to treat everyone's situation as unique solely because everyone occupies a different point in situation-space, it is possible for two things to be so similar they might as well be the same. The postmodern argument of "the death of the subject" asserts that most of the new, trendy, avant-garde styles of writing like Hemingway, Fitzgerald, or Pound have all been claimed, and now there are fewer and fewer writing styles - and even personalities - that could seem new, that is, significantly different enough from an already extant style (or personality) to be considered "unique". Because of this, individuals claiming to have unique personalities largely tend to conform to a particular subculture, adopt that subculture's values, morals, and expectations, and thus, our personalities become so similar to others they start to seem derivative. Yes, there are many different subcultures, cultures, morals, and truths - but there is indeed a finite number, and you as an individual will end up either conforming to one of these societies or becoming a hermit.
If personalities can work this way, and personalities are taken to be a consequence of "situation", then people's situations are most likely also similar enough to no longer be considered unique, and thus, you could very well be in the same situation as others. Not everyone is in the exact same situation, but there could be a very small (relative to the entire population of humans) number of possible distinct situations, meaning that pretty much nobody is in a "unique" situation.