When the Falcon Heavy was launched on it's test flight, what was the only part of the operation that failed?

The story behind the answer

Center Core Landing is correct because during Falcon Heavy’s first test flight (Feb 6, 2018), everything else worked: ignition and liftoff were smooth, “Starman” in the Tesla Roadster was deployed to a heliocentric orbit, and the two side boosters performed a dramatic synchronized touchdown on land. The center core, however, failed to land on the droneship when only one of its three engines relit for the landing burn—reportedly due to insufficient TEA‑TEB igniter—so it hit the ocean near the ship.

This flight still marked a milestone for heavy-lift reusable rocketry, with the twin booster landings becoming an iconic image of modern spaceflight. To remember it: think “twins nail the landing, the middle misses”—two side boosters home, center core overboard.