Mistakes like this are surely often based on assumptions - in fact we lost our kid in the woods recently by assuming she'd be trailing behind us like she normally does, running to catch up every now and then, but in fact she'd taken a completely wrong path we'd never have assumed she would take. Of course if the hand seems in trouble - you're going to miss the flight - you make the assumptions you need to enable you to make the contract or the flight, perhaps each parent assumed the other, or the other kids, would be taking care of the missing one.