A “How Long Is the Coast of Britain?” alike answer to estimating how long software development will take.
Let’s take a hike on the coast from San Francisco to Los Angeles to visit our friends in Newport Beach. The line is about 400 miles long; we can walk 4 miles per hour for 10 hours per day, so we’ll be there in 10 days.
One day later:
Wow, there are a million little twists and turns on this coast. A 40-mile day will barely get us past Half Moon Bay. This trip is at least 500, not 400 miles.
And it gets even better as the trip continues …