By Richard Curtis If you do something so horrendous as to provoke your agent to declare, "Life is too short," you'd better start looking for someone else to handle your work. It means you have tried his or her patience beyond its limit. You're a walking dead author. We recently described good timing as one of the most important virtues a literary agent can bring to the job. There's another that most good agents possess, and that's patience. If timing is the art of "when to," patience is the art of "when not to." Unfortunately, that often means when not to knock my head against a wall, wring an author's throat, or hop in a taxi, race over to a publisher's office and trash it. Although some people are born patient, for most of us it's an acquired quality. We attain it only with experience, and it is arguably the only significant benefit of aging. If you are constitutionally incapable of practicing patience, you are definitely no