The Marketing and AdsOptimization bounded contexts both subscribed to the CRM’s domain events and ended up implementing the same projection of the cus‐ tomers’ data. In other words, the business logic that transforms incoming domain events into a state-based representation was duplicated in both bounded contexts, and it had the same reasons for change: they had to present the customers’ data in the same format. Therefore, if the projection was changed in one of the components, the change had to be replicated in the second bounded context.

That’s an example of functional coupling: multiple components implementing the same business functionality, and if it changes, both components have to change simultaneously.