Trying to dig up the source for this quote leads to quite an array of people it's been attributed to! So far I've turned up variants sourced to: Abigail van Buren (the old name of "Dear Abby"), Johann Wolfgang von Goethe, a Reader's Digest letter-writer named James D. Miles, and Malcolm S. Forbes. Most of the attributions are questionable, though (e.g. I haven't found anybody actually pointing to where in Goethe's works such a quote can be found).