It depends on the situation. The concept itself should hold true from the smallest to the most extreme sense.
at a cost of another.
Could be as simple as keeping the extra dollar that was from incorrect change. Just because it's small doesn't mean it's insignificant. And how can that not be applied towards defending ones family from harm? One can justify that we are only fighting evil. People find reason to justify their actions; actions that benefit themselves. This is, in effect, finding the best way to survive for the current situation.
What you are putting forward, however, is the benefit of having foresight. I wholeheartedly agree. Unfortunately, not everyone has this or the situation just doesn't allow enough time for it's fruition.