Half of this is understanding the probabilities of certain things happening. This involves estimation of both known and unknown unknowns. The other half is knowing how to keep things flexible without having to write a lot of extra codes. Where are the architectural choke points to apply the tourniquet to allow for later expansion?
Aside from being an expert in abstraction, domain knowledge is also a key component to make these decisions. You're right that it takes years to become competent at it, and even then there's a good amount of luck involved.
Aside from being an expert in abstraction, domain knowledge is also a key component to make these decisions. You're right that it takes years to become competent at it, and even then there's a good amount of luck involved.