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The book says that the main reasons behind most of the software projects failures:

1. Incomplete Requirements:
The design and the implementation may start before even the requirements has been completed or signed by the customer.

2. Ambiguous Communication:
When the communication between the team members is ambiguous. The way the application which will be developed will be also ambiguous.

3. Architecture Problems:
It has 2 sub problems:
3.1. Complex Architecture:
Complex architecture may be hard to understand by the team designers. So wrong low level design and implementation may occur.
3.2. Inflexible Architecture:
When the architecture is not extensible. It will be very hard to accommodate with the new customer requirements.

4. Undetected Inconsistencies with External Systems:
Interfaces with external system should be well-defined before going into implementation to prevent “Developing the wrong system”.

5. Waterfall Model:
Waterfall model cannot succeed with customer software services. Customers always want to give their feedback periodically so Software models that are based on iterations and milestones are the most recommended with customer services. The (Rational Unified Process) is one of these software models.