Practice — Case Study: Video Recommendation (YouTube / Netflix-style Homepage) (5 questions)

You are designing the homepage ranker for a video platform. A colleague proposes optimising purely for click-through rate (CTR), arguing "clicks are abundant, easy to log, and directly measure whether a user wanted to watch the video."

1. Explain the specific failure mode this objective produces in production.
2. Propose a better objective and justify each signal you include.
3. Describe how you would validate that your chosen objective actually serves the business, given that offline metrics cannot fully verify it.