It's not all that "hard" but why do CFIT accidents happen to IFR rated pilots so often? Because they're human, statistics don't lie, the whole 178 seconds to live thing isn't just a ploy to get non rated blokes out of the muck cos it's so much fun being in it, it would be even easier if every airfield in the country and track was at sea level, terrain was non existent and icing was never an issue. It's the old swiss cheese principal, an aeroplane doesn't just decide that in cloud it don't wanna keep flying wings level, factors combine to give the effect, not trusting the instruments (A human factor issue), not knowing where you are (Spatial awareness), not thinking ahead of the aircraft (See previous). On the issue of instrument reliability see an old accident file on a Westwind that went in to Botany Bay in 1985 (ish) think the rego was IWW or something similar, was doing a departure to the south on a moonless night, simulated AH failure, just so happened the captains actual AH DID fail, went inverted and spun in. A Westwind isn't too badly equipped.