The database example gives that line a practical test: can you explain why the endpoint is slow and check whether the fix helped? Much clearer than measuring knowledge by how much syntax someone remembers.
Exactly. And sometimes the query isn't even the real problem. In PostgreSQL, bad row-count estimates can push the planner toward a poor join strategy, so adding an index won't necessarily fix the endpoint. You need to look at the actual execution plan, compare estimated vs. actual rows, and measure the change under realistic data. AI can suggest the fix, but you still need to know what evidence would prove it worked.