Med Service by Murray Leinster — Read

"The probable complete success of a human enterprise which affects non-co-operating other human beings may be said to vary inversely as the fourth power of the number of favorable happenings necessary for complete success. This formula is admittedly empirical, but its accordance with observation is remarkably close. In practice, the probability of absolute, total success in any undertaking is negligible. For this reason, mathematics and sanity alike counsel the avoidance of complex plannings, and most especially of plans which must succeed totally to succeed at all. " _Probability and Human Conduct_ Fitzgerald

When morning came, Calhoun very wryly considered the situation. He couldn't know the actual state of things, to be sure. He'd been shot at. But even so -- though that fact did not allow his hopes to be realized in every detail -- the probability of a considerable success remained. It was not likely that the invaders would ascribe the finding of unconscious, stertoriously breathing members of their number to Calhoun. Making men unconscious was not the kind of warfare a plague-refugee would use. Still more certainly, it was not what the invaders themselves would practice. To devise and spread a plague, of course, was not beyond them. That had been done. But they would not disable an enemy and leave him alive. They would murder him or nothing. So when men of their group were found in something singularly close to the terminal coma of the plague, they'd think them victims. They'd guess that their supposed immunity was only to the early symptoms, not to the final ones and death.