This is a joke, though it also could be considered a parable:
A Mafia Godfather is missing around $10 million in cash and eventually discovers (through the process of elimination) that Guido, his bookkeeper, is responsible for the theft.
Now Guido is deaf, and that has a lot to do with why the mob boss hired him in the first place. The boss had made the simple assumption that Guido would never hear anything incriminating, so he'd never flip and testify against him (yes, Guido still had incriminating knowledge from doing the books, but hey, this is a joke...)
The Godfather brings along his consiglieri, Luigi, who knows sign language, to confront Guido about the missing $10 million. Why does the consiglieri know sign language? Because the Godfather doesn't. To explain as swiftly as possible: the boss knew he'd need to communicate with Guido occasionally, so he had ordered Luigi to learn to sign. The boss could have told Luigi, "I'm too busy" or "I don't have time, etc.", but the simple fact was the boss didn't have the slightest interest in learning sign language. There were 100,000-plus things he'd rather do. And it was only fitting that Luigi learn since Luigi, a good consiglieri, was the first man to point out this potential problem.