I don't suppose this is a new theory, but I've never heard it stated quite this succinctly.
One kind of difficulty is when the shots themselves are hard - for example, off of a downhill lie to an elevated target, or a long iron to a firm, crowned green.
Another kind of difficulty has to do with the consequences of a bad shot, such as water, sand, or some other situation from which scoring is difficult. Executing the shot correctly, however, might not really be that hard. An island green on a calm day would be the extreme example.
The Stadium Course at PGA West has always intrigued me in this way. The shots themselves aren't really that difficult: flat lies, nice grass, ample targets. Plenty of guys in Q-School cruised around in 70 shots or fewer the last few days.
Yet it's always on the lists of everyone's hardest courses, because the consequences for missed shots are so bad.
Obviously the hardest courses combine both kinds of difficulty - shots that are hard to execute, with severe penalties for not pulling them off. Oakmont seems like the poster child for this.
Am I on to some significant distinction here? Or does it exist already by another name?