Our most-shared feature was a bug that made our product slower.

We shipped a caching bug that made one page load in 2.1 seconds instead of 0.4 seconds. It was live for 6 days before we caught it.

In those 6 days, we saw something strange. Users on that page were spending more time on it — median 4m 20s versus 1m 10s normally. They were also sharing it more. Shares of that page rose 340% during the bug window.

We investigated. The slow load meant the page rendered progressively, and users could see sections appear one at a time. They were reading it differently. They were not waiting for the whole thing. They were consuming it in pieces, and the pieces were more digestible.

We rebuilt the page to render in deliberate stages even when fast. Time on page rose to 3m 40s, and shares rose

180% — less than the bug, more than the original. The bug had accidentally shown us how people wanted to read.

What accidental behavior in your product have you fixed before you understood what it was telling you?