Red Queen Risk
Part Of
A more specific formulation of Schedule Risk is Red Queen Risk, which is that whatever you build at the start of the project will go slowly more-and-more out of date as the project goes on.
This is named after the Red Queen quote from Alice in Wonderland:
“My dear, here we must run as fast as we can, just to stay in place. And if you wish to go anywhere you must run twice as fast as that.” - Lewis Carroll, Alice in Wonderland
The problem with software projects is that tools and techniques change really fast. In 2011, 3DRealms released Duke Nukem Forever after 15 years in development, to negative reviews:
"... most of the criticism directed towards the game's long loading times, clunky controls, offensive humor, and overall aging and dated design. " - Duke Nukem Forever, Wikipedia
Now, they didn't deliberately take 15 years to build this game (lots of things went wrong). But, the longer it took, the more their existing design and code-base were a liability rather than an asset.
Personally, I have suffered the pain on project teams where we've had to cope with legacy code and databases because the cost of changing them was too high. This is shown in the above diagram: mitigating Red Queen Risk (by keeping up-to-date) has the Attendant Risk of costing time and money, which might not seem worth it. Any team who is stuck using Visual Basic 6.0 is here.
It's possible to ignore Red Queen Risk for a time, but this is just another form of Technical Debt which eventually comes due.