Traditional waterfall model TREATS Analysis, Design, Coding and testing as discrete phases of a software project.

QUALITY Suffers:

First, the project runs out of money until it reached the last phase. This means that a good project tends to cut on the testing phase and the quality suffers.

Poor visibility:

Secondly, because working software isn't produced until the end of the project, you never really know where you are on a Waterfall project. That last 20% of the project always seems to TAKE 80% of the time.

Too risky:

Thirdly you've got schedule risk because you never know if you are GOING to make it until the end. You've got technical risk because you don't actually get to test your design or architecture until late in the project. And you've got product risk because don't even know if you are BUILDING the right until it's too late to make any changes.

Can’t make changes in the middle:

It’s not easy to make any changes in the middle because the architecture and all technical aspects are already closed before the development phase. It is very costly to do those changes in the middle.

The Agile Approach:

Instead of treating these fixed stages Agilists believe these are continuous activities.

By doing them continuously:

• Quality improves because testing starts from day one.
• Visibility improves because you are 1/2 way through the project when you have built 1/2 the features.
• Risk is reduced because you are getting feedback early, and
• Customers are happy because they can make changes without paying exorbitant costs.