As kids it's drummed into us that being selfish is wrong.
Share your toys. Share your food. Share the airtime in conversations.
Of course this is pretty sensible guidance because living with others in relative harmony means not keeping it all to yourself. The theory is that if you share with others, then they'll share with you too.
But not being selfish isn't the same as believing that it's somehow wrong to care for yourself, and to look after No 1 at times.
When you travel by air the safety demonstration makes clear that you should put on your own oxygen mask before tending to the needs of others, and this makes great sense.
If you're going to be of help to the people around you, you need to be strong yourself.
So making sure you're well-rested, well-fed and well-adjusted isn't selfish.
It's just right and proper.