Listing architectural assumptions
Just as it is important to have a clear understanding of the guiding principles, it is equally important to have a clear understanding of the architectural assumptions that you make while defining your architecture.
Defining architectural assumptions is a very system-specific task. For example, you may assume that all your business services are always accessed via a service gateway and therefore do not need to have explicit authentication mechanisms incorporated. Authentication will happen at the service gateway level.
Another example of assumption is when you know that you have a separate authentication provider that you will always use for any authentication- and authorization-related claim. In this case, you should clearly mention this in the assumptions list.
Clearly understanding the assumptions, the reasoning behind those assumptions, and their implications on the system as a whole, will greatly reduce your stress levels in terms of dealing with people...