Bill Tuccio writes for StickyMinds.com about similarities between a flight plan and a development plan:
In the world of software, there are those projects where the weather causes low visibility. The overall flight plan is just as important, but the exact route to be followed cannot be defined due to changing conditions. In these cases, the exact route can only be determined by getting started and reacting to conditions through observation and measurement. In fact, certain conditions cannot be known until you are under way. If you delay in an effort to acquire requirements that are so absolute that the path is completely defined, you will never depart.