When I wear glasses people compliment me by saying, "My, but don't you look intelligent!

When I wear contact lenses people compliment me by saying, "You sure look nice but you should do something to improve your ability to think. Here, this book should do it!"

After reading the it, I put on my glasses and return the book. Immediately I get complimented. -- "I'm so happy to see that the book succeeded in improving your mind. Too bad it had to spoil your looks in order to do it."