It's not really THAT complicated, in theory. But it does emphasize the necessity for CBs to effectively play "off" technique: they're each initially reading more than just the WR lined up across the LOS, so all the DBs need to see the entire pass play develop and of course react appropriately, in unison.
If a slot WR runs an out-and-up route (a kind of double-move), for example, that puts pressure on the boundary CB AND the corresponding safety, whose initial reads can be exploited through no fault of their own.