Once upon a time, a man passing by a river noticed that a grown-up man was going to throw a child he carried in his arms into the river.
At this moment, the child was frightened, crying loudly and shouting in confusion.
The passer-by asked:
"Why are you to throw the child into the river?
Aren't you afraid he would be drowned?"
The man answered:"It doesn't matter. His father is good at swimming."
The passer-by then asked:
"His father can swim, but does it follow that the son can also swim without practice?"