Living within a day’s driving of the majority of the AT, I have had the opportunity to take several hikes on the trail. Spread over time, they have taught me a lot.
If my first section hike last year had been the beginning of a thru-hike, I would have dropped out like the majority. After 5 days, I had a large blister, lots of other wounds on my feet, and knee pain that would not quit. It took two weeks to get over that knee pain. :bawling
I made some changes, (poles and glucosamine), and was able to do a 3 day hike in much better comfort. A later 4 day hike helped to shape some opinions about equipment and shoes. 
This summer I plan a 2 week section to learn more lessons. I will also be doing a couple other week long sections. For me, this is the sort of confidence building and experience building that has helped me to understand long distance hiking’s effects on me and my equipment. (I also have lots of vacation time to burn this year.) :boy
The only downside (if it is one) is that I have begun to realize that my plan is no longer to do a thru-hike, but to just finish the long (~1500 mile) section next year. I have fallen in love with long distance hiking, not thru-hiking.
The potential upside, is that I may reach Katadin, wanting to hike more, not finished with long distance hiking, but just beginning. :tongue
risk