The Log Line That Took Three Days to Find

One missing field in a JSON response. The code had a fallback that defaulted it to null, and the frontend rendered it as empty without an error. No crash, no stack trace, no warning.

I added logging at every step of that flow. Found it in twenty minutes.

Now I log the shape of data, not just the values. What keys exist, what types they are. It catches the silent stuff.

What silent failure cost you the most time?