One of the most common causes of heel pain is plantar fasciitis. Plantar fasciitis is an ailment that results from a swollen or weak plantar fascia in the foot. Plantar fascia is the tissue that connects our heel to our toes. When it becomes inflamed, irritated or weak, you are going to experience pain each time you take a step. And the worse the condition becomes, the more walking or running may seem intolerable.