The saying goes something like "Put on your own mask before you help someone else put on theirs." Referring to the situation where the plane is crashing, and oxygen masks pop out of the ceiling as the cabin depressurizes. You'd have to first secure yours, lest you pass out while trying to help someone else secure theirs.
The metaphor is for tough situations we encounter. It seems it could also be used for ethical questions. For example, suppose for a moment that you are fortunate enough to have some choice over what work you're going to do day-to-day and be paid for. On the one hand, you can go for something that's personally engaging. But maybe doesn't do much to help the folks in the worst shape. Think: something like professional poker. On the other hand, you could be spending nearly all your time among the poor, or working in a skilled trade and volunteering time and money to causes like sheltering homeless youth.
Where the metaphor applies is that the second case may be very draining to you, leaving you unable or unwilling to help. Metaphorically, you helped someone else fasten their oxygen mask before you fastened your own. You passed out. You became unable to continue helping that person, or doing anything for that matter.
Whereas, had you gone for poker, that might have been more like putting the mask on. You win some money,you donate it. Or maybe you try to help people by writing a book about decision-making. And yet: in the metaphor, putting your own mask on before or after you help someone is binary and discrete. And in our ethical choices, like choosing where to put our time, it's more continuous - a question of how much oxygen we need to give ourselves before we start helping others.
Maybe we just need a bit of air. At the risk of torturing the metaphor, poker is a full tank, blasted direct into the lungs, and something like nonprofit work still gives you just enough air.
Here's another example: you want to give to charity, but you'd also like the instrumental utility of having money that gains passively, like in an investment. Do you aim for FIRE (or paying off debts)? That leaves you with time and perhaps money to donate, but not for a while. In contrast, you could set up a recurring monthly donation. Or you could do like an early Christian, and give it all away. Put on your mask first, try for both at once, or put on theirs first?
There is such thing as too much oxygen,or at least improperly-managed oxygen. If we follow the analogy, this can be more likely to happen when you submit to experimental conditions-ignoring wisdom of tried paths, trusting experts or supposed authorities too much. For example, you got into tulip-speculation in the 1600s with the intent of making a fortune and then helping the needy.
This leaves us with supplements to the metaphor, assuming one goal is to help others.
- Put your mask on first or else you'll pass out. Even putting your own on is going to be hard.
- Take a breath, but don't dwell on how much you need to be breathing before you help your neighbor. The oxygen flow is automatic now, and your body will figure it out or it won't.
- Put you neighbor's mask on.
- Move to the next person who needs help but if someone's already helping, don't fight them on it or try to correct them, unless you know you're more qualified (e.g. a doctor or aerospace engineer)
I leave it to you to determine what doctor/aerospace engineer compare to in the metaphor.