I assume zmj's point is that we implicitly make this trade-off all the time. For example, cars could be safer, but then they would be more expensive. Anytime we opt for a cheaper car with less safety features, we are making a cost-benefit analysis involving our own lives and the lives of the people who will travel in our car. (Who are probably the most important people to us.) There becomes a point where the actual gains in life-saving potential is negligible, and we don't think it is worth the cost. But we rarely state it that way.