I like to use a political analogy.

Even in the best years US airlines had profits less than 10% of sales (a rather thin margin). In the pool of travelers, there are those loyal to one airline or another (either through corporate contracts, elite status, or hub city) and there are those who are leisure travelers looking to fly cheaply even if it means not getting miles or making a connection vs non-stop.

This second group, as I have defined it above, will fly on anybody and will make their decision when they see the price.

The first group is loyal and worth more to the airline, but it is the leisure passengers (think swing voters) that will provide the revenue to make an airline swing to a positive margin.