If you are juggling, for example, 10 planes, each with 150 passengers on board, and one of them is already 30 minutes late, and the others are on time, it's tempting to say that you should prioritise the late flight. But if that means making all the other flights a little late, or one of the other flights a lot late, it's probably a worse outcome for the airline and most of its passengers. 150 people are already late and angry. If they are a little later, they probably won't be much angrier. If you make an extra 150 people very late, then you end up with 300 people late and angry. Or you could make an extra 1350 people a little late and, depending upon the circumstance, you leave all 1500 people with a bad impression of your airline.