This post is from the ATC website:

Here are some interesting facts...

From the Appalachian Trail Conservancy website-

HOW HARD IS HIKING THE APPALACHIAN TRAIL?

Hiking the entire Appalachian Trail is a grueling and demanding endeavor. It requires great physical and mental stamina and determination. The terrain is mountainous for its entire length, with an elevation gain and loss equivalent to hiking Mt. Everest from sea level and back 16 times. The treadway in many places is rocky or filled with roots or mud. Maine and sometimes other states require fording of streams that can be hazardous after heavy rains. Sections that could be described as flat or smooth seldom last long.  

Because the window of time in which a northbound thru-hike can reasonably undertaken without specialized winter gear is limited to about seven months, the saying "No rain, no pain, no Maine" has become an apt mantra. Those who are physically fit may have an edge, especially in the beginning, but ultimately completing the A.T. is more of a mental challenge. The Appalachian Trail has been hiked by people ranging from age five to 86 and by hikers with a wide range of disabilities.

IF HIKING THE APPALACHIAN TRAIL IS SO HARD, WHY WOULD I WANT TO DO IT?

Walking the entire Appalachian Trail in a continuous journey is one of the most rewarding, exhilarating, and memorable ways you can spend six months of your life. Thru-hiking enables you to immerse yourself deeply in the natural world and view some of the most beautiful, wild and pastoral landscapes in the United States. Thru-hiking will also give you the opportunity to form friendships with people of all ages, from all walks of life, and from around the world.

14 states, 6 National Parks, 8 National Forests, a few Wilderness Areas, and over lands managed by more than 30 other state and federal entities?  Not to mention 31 volunteer trail clubs.