Surely there must be some commonality! Even if it is one we have yet to identify. Perhaps I ought speak more with our fellow non-natives and learn something of their homes...

[Based on his personal experiences trying to call just one person across the rift, each person he had mistakenly called was still personally connected to his true target in some way! Not that he's about to mention his efforts in other-wordly summonings at this particular juncture.

Then, however, his brow furrows and he gives Takame another once-over. Now, that's interesting, especially from someone who he had assumed to be from the First.]

The existence of Hydaelyn's shards is not common knowledge.