"Great news, Mr. Smith," the psychiatrist reported. "After eighteen months of therapy, I can confidently pronounce you completely cured of your kleptomania. You'll never be tempted by such desires again."
"That's great, doctor," said the patient with a sigh of relief.
"And just to prove it, I want you to stop off at Comet on the way home and walk the length of the store. You'll feel no temptation whatsoever to shoplift."
"Oh, doctor, however can I thank you?"
"Well," suggested the doctor, "if you do have a relapse, I could use a microwave."