Once upon a time, a boy who was called Stephen lived in a small town which was a long distance from the sea. Stephen read a lot of books about ships and their voyages to distant countries, and he always imagined himself in each of them. When he was sixteen, he decided that he wanted to become an officer in the merchant navy, so he went to a place which trained young men for these jobs. Stephen enjoyed the lessons very much, especially the ones on a ship, and he was also glad to do a lot of sports and exercises, because he had always been very fit, and by far the best in his school at such things. Then one day one of the teachers informed the new students that it was time for them to begin having swimming and diving lessons. Stephen arrived at the pool the next morning with the other students. He was looking forward to learning to swim. The teacher arrived a minute later, and commanded those who could not swim to go into one group, those who could swim but not dive properly to go into a second group, and those who could both swim and dive well to go into a third one. Stephen went into the second group. The teacher then told the students in the second group to go down the steps into the swimming pool one by one and swim to the other end. The first two obeyed, and neither of them had any trouble in swimming to the other end. Stephen was the third in the line. He climbed down the steps, but as soon as he began to swim, he sank under the water. When he did not come up again, the alarmed teacher jumped in and dragged him out while the other students cheered. Then the teacher said to Stephen, 'Why ever didn't you join the group that can't swim?' 'Because I'd never even bathed in a pool before,' Stephen answered, 'so I didn't know whether I could swim or not.'