Two Truths About Estimation
The first truth about large software projects is that it’s nearly impossible to provide an accurate estimate at the outset. A modern web site is a collection of small systems interacting to form a much larger system — one that is often about as predictable as the weather, or the stock market. In scientific terms, an enterprise-scale Drupal website is “fundamentally complex,” and fundamentally complex systems tend to defy prediction.
The second truth about large software projects is that clients almost invariably require estimates, whether it’s a fixed bid or a “back of the envelope” guesstimate they can take to their superiors to get an Agile project the green light.