Here are some thoughts based on 35 years of hiking on the AT. (not continuously)
1. Hikers attempting to thru hike are not rock stars. Don't expect/demand special treatment on the trail or in town. Your actions and behavior will impact all hikers who come after you.
2. You are not a thru hiker until you walk your last mile. Until then you are nothing more or less than a hiker, section hiker, or what ever other classification you want to put on it. So don't treat others who have not declared themselves as thru hikers any differently. Statistically the odds are not in your favor to be successful in completing your thru hike.
3. Long distance hiking is not easy. If it was everyone would/could do it.
4. Respect and love the trail. Stay on the footpath, don't cut switchbacks, LNT, etc. Thank any trail maintainers or trail clubs you see. Without them there would be no trail. Don't bitch about the PUD's, trail conditions, etc. The clubs and maintainers are volunteers and doing the best they can. After you get off the trail, join the ATC or local club if you are not already a member. Do some trail work.
5. Enjoy yourself. Everyday will not be filled with sunshine and spectacular vistas, but after you get off the trail you will treasure every day spent on it. Several years ago while doing some trail maintenance on White Cap MT in ME I ran into a 60 something thru hiker. I asked him how his hike went and if he was excited to be almost finished. He said he could not wait to finish and hated every day he hiked. I asked him why he continued and he said he was military and he always finished something he started.
6. Don't believe half of what you read on this site. Many of these posters are right and they know it.