In real life, cost-benefit analysis typically works similar to business plans. First you decide what you want to do. Then you write up a case supporting that.

In real life, cost-benefit analysis typically works similar to business plans. First you decide what you want to do. Then you write up a case supporting that. In doing so, you make lots of wild guesses and make sure that + ones use the high side of the guestimate range, and - ones use the low side of the range. Remember, there was a business case and cost benefit analysis for pets.com and nearly every other internet failure that justified everything they did to investors. This is the real limit of these analyses.