To thru hikers and others who've backpacked for significantly long distances, what was your biggest surprise, your most unanticipated difficulty, or your highest learning curve on your long-distance hike? I've hiked about 500 miles total in sections from 20-90 miles at a time. I'm planning on a thru-hike starting in April. Your responses will help me anticipate things I need to pay attention to. Thanks!