An ML engineer on the team flagged something odd about a subgroup readout from a category-page experiment, and the question that followed turned into one of the cleaner real-world illustrations of encouragement design I've worked through — the framework for experiments where you can't force exposure to a treatment, only make it more likely. This is that walkthrough, numbers changed, names removed.
The Setup
A category browse page shows product cards, and a subset of products have an animated GIF preview instead of a static thumbnail...