Hm, I'm not convinced yet. I think the problem here is the notion of a bad habit and at what point it becomes difficult to break. I'll use your example: I was trained in OWD on my knees mostly. I did teach myself trim, buoyancy and hence to dive in a horizontal position. I also kept practising skills, so I am now perfectly able to take off my mask, clear it or switch to a backup mask all while in trim and without significant changes to buoyancy. Same goes for air sharing, finning etc. Yet, I'm absolutely certain I will be able to make adjustments and changes to how I do that if shown a better way to for example store and unclip my spare mask or the order in which to do things etc. Those are details. But the basic skill is there. The comfort doing them is there. Maybe other people struggle with this and it's just that I am used to learning things and have a good sense of my body in space. Or everyone is like that. I have no idea. But I have zero doubt I will be a better fundies student having practiced those things even if I need to improve and make adjustments. However, we are talking about a few months of diving and practicing things. We're not talking about a diver who has done things "wrong" or inefficiently for 10 years. Maybe that's where the difference lies.