Start here. This is the direct spoken answer to practice first.
Why this question matters
Interviewers use failure questions to distinguish honest ownership from polished success stories.
Use this as an adaptable model, not a story to claim as your own. Replace the project, constraints, your actions, collaborators, outcome, evidence, and reflection with truthful details from your experience.
I led a change that moved a slow reporting workflow to precomputed results. The reports became faster, but we had not understood how much users depended on seeing newly entered data immediately. Adoption dropped because people did not trust the freshness of the result. I paused the rollout, restored the previous path for affected users, and spoke with them to understand where the design had missed the real requirement.