The biggest lie we tell ourselves in software engineering: "The feature is 90% done, it just needs a few tweaks."

I’ve built streaming platforms, real-time messaging apps, and custom APIs. Getting the happy path to work usually takes a few days.

That last 10%? It takes four weeks.

Here is what that "last 10%" actually looks like in production: • Handling intermittent network drops without breaking the UI state. • Writing graceful rollbacks for when a third-party API fails halfway through a transaction. • Building internal admin tools so non-technical users don't need you to manually run SQL queries to fix their data. • Patching race conditions that only appear when 50 users hit the same endpoint simultaneously.

True production readiness isn't about feature completion. It's about failure handling.

What is the single most annoying 'last-mile' edge case that turned an almost-done feature into a multi-week headache for you?