^As a rule, any attack against the Borg only works once. They don't anticipate unforeseen possibilities, so you can always get in one or two hits with an attack they haven't faced before. But once they've seen it, they can adapt to it and it can't be used again. That's been the standard pattern for Borg engagements from the very beginning.
The problem with that idea, though, is that it tends to be portrayed as though the first time Starfleet attempts a particular maneuver against the Borg is the first time anyone has ever tried it. Realistically, if the Borg have been around for millennia, assimilating thousands of civilizations, then anything Starfleet tries -- certainly something as obvious as beaming a torpedo aboard -- should've been done already, and the Borg should've already adapted to it.
The problem with that idea, though, is that it tends to be portrayed as though the first time Starfleet attempts a particular maneuver against the Borg is the first time anyone has ever tried it. Realistically, if the Borg have been around for millennia, assimilating thousands of civilizations, then anything Starfleet tries -- certainly something as obvious as beaming a torpedo aboard -- should've been done already, and the Borg should've already adapted to it.