A messy release taught our team this lesson better than any architecture meeting. We added a loyalty feature, and it unexpectedly affected checkout discounts and reporting because everything was too tightly connected. Later, when we planned the next version, we looked at Modular Architecture for Software Development to explain why each feature area should have cleaner responsibilities. I liked that approach because it was not just theory; it gave us language for discussing boundaries, dependencies, and testing. For teams adding features often, I would recommend reading something like that before the product becomes too tangled. New features still need careful QA, but if the system is modular, one change is less likely to ripple through every screen, service, and database rule.