Continuous Software Maintenance aka Agile Software Development

Its widely accepted that about 40-90% of the total cost of an application is incured after it goes into production, the phase that is traditionally called maintenance.

When I'm doing Agile, not the practice-oriented farce kind, but the values-principles-oriented real kind, I don't build software in phases. I develop software in a continuous flow of activities. When I'm doing this, it feels like I'm continuously maintaining the software instead of only maintaining it after its done, and that makes all the difference.