Come up with a real-world problem in which only the best solution will do. Then come up with one in which a solution that is “approximately” the best is good enough.

Only-the-best: The methods and procedures used by surgeons during life-saving operations must use only the best available approach given the current understanding of medical science. Lives are literally on the line.

“Approximately”-the-best: The algorithm used by a cashier to determine proper change for a purchase need not be efficient, so long as it produces the correct figure.