I've had to teach some mentally challenged helicopter pilots in recent years, but I've found there is always a way to explain something to someone who doesn't understand your first explanation, or second. So here goes...
Hang that 10m long line on the nose of your 10m long helicopter. The way it might flail around in flight if it goes aerodynamic it would probably fly pretty close to the tail rotor, but not actually hit it. Now go and hang that same line on the hook of the same helicopter. Bingo, now that rig is potentially flying within range of the tail rotor.
I've dinged the underside of the tail boom a few times after loads hanging off 20' or 30' lines have fallen out of nets rigged by qualified load masters, but lucky they were all in B212 or S76 and the tail rotor, being bolted on top of a pylon, was out of range. Had I been in a B206 or AS350 it may well have been a different outcome.
As for said new pilot by way of example I would say, refer to the external load section of the operator procedures manual, the RFM, and the role equipment OM, and take heed of what they say.