Many people each day come into our office here in Worcester Massachusetts with problem with their heels.  Plantar fasciitis is by far one of the most common problems a podiatrist sees. In order to explain this condition to patients I have simplified the approach to three main contributors.
1.  Inflammation of the fascia on the bottom of the heel
2.  Tightness in the back of the calf region
3.  Unstable foot position
The reason many people only get partially better and the condition returns is because only one or two of these areas are treated.  For example, many people with only some mild symptoms such as pain getting out of bed in the morning try stretching and the foot pain goes away only to return in the future.  
If you want to learn more about this condition and the three contributors and treatment options take a look here:
To your health,
Dr. Donald Pelto