It was one of those checks that should’ve taken thirty seconds. I ran a search against a real list — a few hundred leads, standard call, nothing exotic — and it just sat there. No error. No result. Just quiet.
I assumed it was slow. I’d built the thing to hit an internal API and page through records, so “slow” was the obvious story, and I believed it for longer than I should have. I even started looking at whether I needed to add caching.
Then I ran the same search on a smaller list — thirty records instead of three hundred — and it worked instantly. That’s when I knew it wasn’t slow. Slow doesn’t have a cliff. Broken does.
The real problem was a single field. My data model marked customer email as an optional, validated email field — which sounds correct, and is correct, right up until the source system’s convention for “no email on file” turns out to be an empty string instead of a null. Pydantic’s email validator doesn’t know what to do with an empty string. It doesn’t skip it. It rejects it. And it rejects it silently enough, deep enough in a batch operation, that the whole search just — stopped. No traceback pointing at the actual cause. Just nothing.
I’d been debugging the wrong problem for the better part of an hour. I was optimizing for a diagnosis I’d made before I had any real evidence for it, and once I’d said “it’s probably slow” out loud, I kept looking for reasons that were true instead of reasons that were right.
The fix was small once I found it — one validator that runs before the email check, converting empty strings to null so the real validation logic still applies to anything that’s actually malformed. Seven new tests to make sure it stayed fixed. But the fix isn’t the lesson. The lesson is that “it’s slow” and “it’s broken” produce completely different debugging paths, and picking the wrong one costs you real time before you even notice you’re on it.
I’ve started treating my own first explanation as a hypothesis to disprove, not a starting point to build on. The five-minute version of that discipline: before you optimize anything, prove it’s actually the bottleneck you think it is.
Next: going back through every other endpoint in the same tool with the same question — not “is this slow,” but “have I actually confirmed that, or just assumed it.”