When drawing a cliff face, I have a hard time trying to make it look realistic. I suppose that’s the hard part: trying to draw naturalistic scenery.
I suppose another thing I dislike about drawing is the depiction of realistically violent scenes. One would think that it would be best not to include them, but I personally think that I should. Too little of them, and you risk turning what you hoped what would be a serious, mature work, into a faerie story, where there’s no pain or suffering. Too much and you could attract attention from the wrong sources. That said, they are extremely hard to do convincingly and from a photograph reference.