This is a great story with many applications:
There’s an oft told anecdote about a medical missionary in a remote place, who watches, in horror, as people give untreated well water to their babies. The children regularly get diarrhea, and many of them die. The missionary explains that, even though the water looks clear, there are tiny, invisible creatures in it that make the children sick. Fortunately, she says, if they boil the water, it will kill these bacteria. A month later she’s back, and they’re still giving the babies the dirty water. After all, if a stranger came into your community and told you that your children got influenza because of witchcraft, would you respond by going out and slaughtering a sheep? Then the missionary has another idea. Look, she says, let me show you something. She takes some water and boils it. See, she says, there are spirits in the water, and when you put it on the fire they flee: those bubbles you see are the spirits escaping, the spirits that are making your children sick. Now boiling water makes sense. Now the babies stop dying. In belief, as in everything else, each of us must start from where we are.
-Kwame Anthony Appiah
Active Philosophy 