It's your DUTY!

When you're flying with small children, why do they tell you to put on your oxygen mask first in an emergency? 

ANSWER: Because the children might not be able to take care of themselves - - - and if you don't take care of yourself first, you might not be able to either. This applies in a LOT of situations.  So, especially if you're going to help others, it's your duty to take care of yourself first.  --L. Reichard White, 1998