We had a bug in production for 16 days. It made more money than most features I've shipped.

+73% revenue. Not from a new feature. Not from a redesign. Not from a growth hack some PM spent three quarters planning. From a bug. A config error that sat in production for sixteen days, silently funnelling every new user in one of our European markets into the most expensive plan. When someone finally noticed, the team wanted a hotfix and a post-mortem. I wanted to see what's in the database. 5% vs 43% Here's what I found. Before the bug, 5% of new users in that market picked the premium plan. That was the normal baseline. Everyone else scrolled down to the cheapest option and hit Continue. During the bug- when premium was the default- 43% kept it. Forty-three percent. The onboarding screen wasn't hiding anything. The price was right there. "Change plan" was one click away. Nobody was forced into anything. Almost half the users just looked at the premium plan and thought: yeah, this works for me. I didn't believe it at first. Classic survivorship bias, right? They selected it, but d