A key question for business architecture in my view. Definitions:
Architecture needs to support the diversity required by a business while controlling the divergence inherent in the people nature of a business.
The way you authenticate a customer will differ depending on the physical channel: phone; paper; web. The way you deal with corporate vs. retail customers are inherently different. These are examples of diversity that the architecture needs to support.
Different ways of logging work are likely to be divergent. Different authentication questions over the phone are likely to be divergent. Different systems for logging customer contacts are likely to be divergent. These are examples of divergence that architecture needs to control.
Why is this important? Because every point of difference within a business is a cost and a risk. Differences require the maintenance and enforcement of multiple processes; they require impact whenever any change is contemplated; they present business risk of non-compliance or less than optimal efficiency or effectiveness.
Diversity requires a business case to support it. Divergence is rarely justified. Know the difference and act accordingly.