you have heard flight attendants explain how to put on an oxygen mask, should it drop down from the ceiling of the plane. “Secure your own mask before helping others,” the warning goes. But the flight attendant does not tell you why. Imagine if you were told that, in the event of a rapid decompression, you would only have ten to fifteen seconds before you lost consciousness. Aha. Then you might understand why you should put your mask on before you help your child. You might understand that if you don’t put your mask on first, you’ll both be unconscious before you can say, “how does this thing
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