What really messes people up is the transition from poor visibility but still in sight of the ground, to not insight of the ground any more. Typically practiced in the sim as a low visibility runway departure. As soon as they start the climb phase, lose sight of the runway, they do a descending left turn and crash in an unusual attitude in the grass off the runway before they've even crossed the upwind threshold. I've seen some pilots do this three times in a row! Crash. Reset. Try again. Crash. Reset. Try again. Crash. Move on to something else. These are not newly minted IFR pilots. They are guys with thousands of hours experience who only see a cloud once per year (and that is in the sim, luckily).