What causes Plantar Fasciitis?

When looking at Planter Fasciitis, people usually fall into two categories. The most common is a foot type that is an overly pronated foot. Which means that the foot is failing to stabilize. This causes a much more mobile foot that probably fails to have a mid-tarsal joint that locks up during the propulsion phase of gait or running. The goal should be to ask what is causing the mid-tarsal joint from locking. Sometimes, it might be just a structural problem. But when a structural problem is present, then orthotics may be the only way to create an environment for the foot to perform efficiently. If not structural then we have to analyze why the foot is over pronating and mid-tarsal joint not locking in gait or running. If the foot does not lock, then the peroneous longus cannot be effective de-accelerating the pronation going to far in calaneal eversion to get back to inversion at propulsion phase. And then the main thing that will be recruited to keep the arch from collapsing excessively is the planter fascia. Plantar fascia cannot tolerate the stress for long. 
Probable suspects of an unlocked mid-tarsal joint would be the lack of dorsiflexion from a limited joint capsule or a tight calf group. Which means that if the foot is ready to propel, but does not have the dorsiflexion needed then the calcaneus will stay everted to help the ankle in dorsiflexion but the plantar fascia will take the stress. Lack of ankle dorsiflexion could also be stemmed from limited hip extension, so the hips need to be evaluated as well to see if there is ample motion to get dorsiflexion of the foot during this propulsion phase. Another probable suspect is the lack of strength of the back butt to de-accelerate heel strike that causes excessive pronation and the calcaneus never has a chance to fully invert for propulsion and/or lock the mid-tarsal joint. 
Basically, these are the main and most probable suspects of plantar fasciitis. A simple functional movement screen can identify the limitations of one’s movement patterns and a few training methods can get the chain reaction of body to function efficiently again