What does Alvarez mean when she says, "making them myth, we lost the Mirabals once more, dismissing the challenge of their courage as impossible for us, ordinary men and women"?

Alvarez means that when people become myths their accomplishments are seen to be impossible, the things of stories and fairy tales. When this happens we feels as we cannot immitate their actions..... that it isn't possible to summon up the same courage in ourselves as they displayed. When in fact, their actions should be emulated.