A recommendations engineer's first experiment tested whether enriching how new, cold-start products get retrieved would help them surface at all. It shipped a result, and the very next planning conversation surfaced two genuinely interesting problems at once: how to design a follow-up that doesn't get confused by new products and established products competing for the same feed slots, and how to explain a metric decline that didn't behave the way the rest of the funnel did...
The Original Experiment
Retrieval for the recommendations feed leans heavily on engagement history — past clicks, saves, and purchases — to decide which products are worth showing...