The question isn’t how difficult a book is, but why it’s difficult. What is it doing with its difficulty? What is it asking of the reader? Does that difficulty reward the reader’s investment of time? You’re entitled, as James Marriott did in the Times, to conclude that in this case the view from the top of Snowdon wasn’t worth the hike. But complaining about the hike per se is to give up on the idea that there might be any case for art that rewards an investment of energy and attention from its consumer.