I was reading Coding Horror today about "Just a Little Bit of Software History Repeating" about the failures of the Denver International Airport and London Heathrow Airport automated luggage systems. Denver's failed baggage system was designed from the inception of the airport and London Heathrow's T5 was installed with the construction of the new T5 terminal. The situations are quite similar to the "complete rewrite" scenario that developer's are frequently tempted by.
It is difficult enough when other people (proposals, marketing, managers, etc.) underestimate the time required for a task or project, but unfortunately developers often vastly underestimate the time required as well. This is well documented in Steve McConnell's classic "Code Complete" and other books as well.
George McFly: Lorraine, my density has bought me to you.
Lorraine Baines: What?
George McFly: Oh, what I meant to say was...
Lorraine Baines: Wait a minute, don't I know you from somewhere?
George McFly: Yes. Yes. I'm George, George McFly. I'm your density. I mean... your destiny.
Learn from the past! Don't be someone's density!