Retracting the landing gear while your plane is still on the ground can ruin your day.
The FHC’s Zero has a safety mechanism built in to keep the gear down while the plane is on the ground. A simple cable runs down the front of the right landing gear strut to the wheel assembly. When the Zero takes off and the landing gear oleo expands, the cable pulls a pin out of the landing gear mechanism, allowing the pilot to safely pull the gear lever to the retracted position.
While the safety helps keep the gear down while weight is on the oleo, the system can be overridden in case of an emergency.