An often-used phrase in project planning is saying the devil is in the detail. Slightly changed and adjusted to business case creation, the same phrase could be “the devil is in the assumptions”  (ref 1)

Project success is often closely related to a few key assumptions such as: revenue is dependent on selling “x” units, costs are dependent on no changes to the standard solution, launch time is dependent on all resources being available when needed by the project.

The realism of a business case is often closely related to the assumptions that are put into it. Often, these assumptions are not made explicit but are built into the figures. They need to be made explicit before they can be reviewed.

If there are critical assumptions built into the business case, it may be important to monitor these closely and to verify they are being met during project execution.

Critical assumptions checklist:

Critical assumptions can typically be related to one or more of the following areas:

1. Priority of project in the organization
2. Ability to make decisions
3. Capability to execute the project
4. Completeness of requirements when the business case is made
5. Customer response to new products
6. User readiness and response to new features
7. Capability of technology
8. Hourly rates
9. Cost estimates
10. Defect rates and time to test
11. Team productivity
12. Resource availability

References:

1. Marty J. Schmidt, 2002, The Business Case Guide – Second Edition, Solution Matrix