When you're asked to provide an estimate, determine whether you'are supposed to be estimating or figuring out how to hit a target.

Quick! How long will it take to send War and Peace over a 56k modem line? How much disk space will you need for a million names and addresses? How long does a 1,000-byte block take to pass through a router? How many months will it take to deliver your project? At one level, these are all meaningless questions—they are all missing information. And yet they can all be answered, as long as you are comfortable estimating. And, in the process of producing an estimate, you'll come to understand more about the world your programs inhabit.