I built a go cart out of some pram wheels, and a few planks of wood. The lane from the farm is steep with lots of bends, so I would listen for cars coming, and if all was quiet, I start rolling down the hill.
Not being particularly old,(nor very bright), I thought a large lump of metal tied to the back would work well as a brake. It didn't. The first time I used it, it about took my head off.
So I abandoned the brake idea, and just relied on listening for cars. Needless to say, I failed to hear one, and met it, full flight, mid corner. Turn sharp right, hit ditch, and go crashing through the scenery, with the go cart flying merrily after me. Frightened the living daylights out of the car driver. That was the end of my go carting days.