Bitterness is an almost universal trait among funny people. They hate it when their friends become successful. They grow positively apoplectic when success comes to someone they consider unworthy. The bigger the success, the bigger the resentment and Leno has attained a level of fame most comics can only dream about. Even more unforgivably, that success came at the expense of more worthy souls: first Letterman and now O’Brien.
Nathan Rabin in Why Some Comics Aren’t Laughing at Jay Leno Essay.