As the plane backs away from the gate, the flight attendant holds up a yellow oxygen mask and says something like this:

“If the air pressure in the cabin drops suddenly, a yellow oxygen mask will drop from a compartment above your head. Put on your own mask first before assisting anyone else.” What they don’t tell us (and I don’t blame them) is why.

If a commercial jet loses cabin pressure at 35,000 feet, most passengers will slip into unconsciousness in less than 30 seconds without supplemental oxygen. If you put your mask on immediately, you can now help others with their masks. But if you help someone else first and they can’t help you back—if they’re a small child, for instance—you could both be in big trouble.

There’s an obvious principle at work here: we must take care of ourselves in order to help others.

Busy, hard-working people rarely find this easy. Self-care—going for a run on a Saturday morning, leaving the kids with a babysitter to catch a movie, scheduling a couple of Think Days—feels selfish. Strangely enough, it’s the opposite that’s true. Self-neglect is selfish, and self-care is selfless.

If you want to help others, first help yourself.