Recount a time when you were knee-deep in a project, but unexpectedly altered course midway. How did you manage this redirection, and what impact did it have on the final outcome?

Interview question asked to Product Marketing Managers interviewing at Zendesk, Clearbit, Square and other companies. Original question asked: Recount a time when you were knee-deep in a project, but unexpectedly altered course midway. How did you manage this redirection, and what impact did it have on the final outcome?.