Product design question

Design a Facebook product for fitness.

Practice this question out loud. An AI interviewer asks it, follows up like a real interviewer would, and scores your answer. Type or speak.

What this question tests

Whether the candidate can find a defensible niche for a new product within an existing social platform rather than cloning Strava or Peloton.

Pick a segment: casual exercisers who want social accountability, not competitive athletes already served well by Strava.
Name the pain point: motivation and consistency drop off without visible social support, and generic fitness apps feel isolating.
Prioritize a social angle unique to Facebook: friend groups and community-based challenges tied to existing Facebook Groups and Events.
Propose a focused feature, such as shared step or workout challenges visible in a user's existing friend groups, not a full fitness tracking suite.
Define success as weekly active participation in challenges and retention lift among participants versus non-participants.

Leverages Facebook's existing social graph and Groups feature as the differentiator, rather than competing directly with dedicated fitness apps.
Chooses accountability and motivation, not tracking accuracy, as the core value proposition, matching a real gap for casual exercisers.
Defines success with a retention comparison between challenge participants and non-participants, isolating the feature's actual impact.

How would you prevent this from becoming another feature nobody opens after week one?
What data would you need from Facebook Groups to build this well?