Lack of gap understanding

1. Most new systems omit critical business rules.

2. Old systems do most of the right things (business rules) but they don't do them the way users want (architecture).

3. Documentation for current business is usually non-existent.

4. People who built and know your system have moved on.

5. The best documentation of how the system works is the code itself.

6. Hard to plan a gap analysis with incomplete knowledge of where you are starting from.

7. Unrealistic expectations based on vendor or IT promises, rather than facts, aggravates the problem.