Good Stuff in There!

Jonathan was getting into the car with a huge smile on his face, and our conversation went something like this:

Me:  That's a huge smile  - I like it.  What's the reason for your big smile?
Jonathan, still grinning:  I don't need a reason to be happy.  I only need a reason to be sad.
Me:  That's a pretty good quote.  Did you read it somewhere, or did you make it up yourself?  Is that original material?
Jonathan:  Calvin and Hobbes.  There's some good stuff in there!