There was an island called Without Sandals.
A budding salesperson from a nearby Town A visited the island and saw that no one at this island was wearing sandals. The salesperson went back to the town and concluded that there are no opportunities to sell any sandals because no one would wear them.
Another budding salesperson from a nearby Town B visits the island and makes the same initial observation that no one in the island was wearing sandals. The salesperson goes back to town and concludes that there is an abundance of opportunity to sell sandals in this island because everyone can wear them.