Usually a sharp pain when pressure is applied to the area of, or around the heel.
The structure of your foot can make it so more weight is shifted to the heel, causing over use and resulting stress in that area.
A proper insole can shift and evenly distribute your weight, relieving your pain.
Image #1- This pain is directly due to the fact that too much pressure is being put on one spot. Improper fitting support will cause this to happen as shown here.
Image #2- With an insole that fits and supports properly, weight is now evenly distributed and spread out.
Image #3- A heel pad is used to provide extra cushion and further disperse the pressure.