Riding mid day with the sun at your back with relatively smooth dunes will get you in trouble as there's no contrast (shadows) and you can launch off a dune without ever seeing it. Check it out next time mid day, face your shadow and look a hundred yards out the sand looks all the same light color, then look 90 deg left or right and you'll see light and dark texture, tire tracks and hi / lo spots. You might be surprised. Better to always be turning and following ridges as they seldom abruptly end and cross over going downhill, you can see way more of the other side than going uphill, gravity assists you downhill and uphill, as an example, as soon as your right front tire goes over the ridge (razor) your left rear unweights and the rear of the quad, and to a lesser extent rail, will want to slide out. Personally, being a quad and bike rider mostly I feel safer at night, I can tell if a rail is coming up the other side by their lights, daytime I haven't a clue till I see a flag, if it's not on a soft springy pole.