A system can keep running long after its structure has stopped serving the business. The symptoms tend to appear in how the team works, well before anything fails outright.
1. Small changes take a long time
When a modest feature touches many unrelated parts of the system, the structure is working against you. Good architecture keeps related things together, so a change stays contained.
2. Fixes cause new problems
If fixing one thing regularly breaks another, parts of the system are more entangled than they appear. That usually points to unclear boundaries and missing automated tests.
3. Only one person understands a critical part
Knowledge concentrated in one person is a risk to the business, not only to the codebase. Clear structure and documentation spread that understanding.
4. Performance gets worse as usage grows
Some slowdown under load is expected. Steady deterioration that hardware does not solve often traces back to how data is stored and moved.
5. Integrations are painful
If connecting a new system always turns into a project of its own, the interfaces between components probably need rethinking.