By the time the Borg attacked Earth in Star Trek: First Contact, Captain Picard was well aware of their many weapons. He had been on the receiving end of a nasty Borg attack in “Q Who,” and he was later assimilated into the Collective before being rescued by his crew.
But what Picard couldn’t figure out was how the Borg Queen survived her Cube blowing up in “The Best of Both Worlds, Part II”.
Eventually, Star Trek: Voyager revealed that the Borg can simply create a new Queen when the old one is killed, and effectively having an immortal evil genius leader is a powerful weapon in and of itself.
As you might expect, though, the Borg Queen would rather avoid getting killed in the first place. And it wasn’t until Star Trek: Picard that we realized that she had an entirely different weapon, one that could help her survive almost anything.