Note: This is the 3rd post in the series around Support Driven Development. If you have the time and wish to start from the beginning, you can find the intro here.
One of the leading reasons a project takes more time than was estimated is because a proper impact analysis was not carried out. In some cases, they may not be done at all. If and when an impact analysis is carried out, rarely is there thought put into how the new development is going to be supported.