Explain a project and justify choices

Walk me through your most impactful project end-to-end: what problem and success metric did you define, what alternatives did you evaluate and reject, and why? Detail how you selected and engineered features (including how you avoided data leakage), your role and key decisions, offline vs. online validation plan, trade-offs you made under time or data constraints, and—knowing what you know now—what you would do differently to improve business impact.