Possibly just too young to have learnt from the school of hard knocks that often comes with age and experience(?) If only the vehicle had missed him and rolled harmlessly away elsewhere, he probably would have learned and never made the same mistake again, but it wasn't to be.
We were out Yerranderie way, and came across a tree down over the road late at night on a gentle incline. I pointed the headlights at the tree and left the engine running so as to not kill the battery, and we set to clearing the tree.
The handbrake slipped and we all managed to get clear and actually hit the brake before the Troopy hit the tree.
To this day I don't leave the driver's seat of any manual with the box in neutral unless it won't move even without the handbrake on (i.e. dead flat or chocked against something), and carry a set of chocks for good measure.