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.

Sorting a catalog is a problem, where only the best solution will do. An "approximately" sorted catalog won't be that useful.

Finding the shortest path between two points in a city is a problem, where good-enough will do. It might not be the fastest way, but you will still get there.