Chicken and the egg. A common problem inviting cognitive overload, drift, and side-effects.
It’s easy to envision final solutions and forget that even basic building blocks have tightly coupled dependencies.
Stubs and mocking help prioritise requirement implementation. And it's critical, service version increases quickly against ongoing development investments.
All whilst maintaining a rigid stance /article/boundaries-in-client-engagement against potentially maybe birthing something other, like an ostrich.