Increasing your body's repertoire of different movement patterns helps safeguard against situations that can cause pain.
If your body encounters some new load or stress, especially for repeated episodes or for a prolonged duration--it's creating an unfamiliar situation with forces against which your body doesn't know how to respond. The magnitude or direction of force may exceed the capacity of what your tissues (joints, muscles, ligaments, cartilage etc.) can withstand, leading to injury. Over a period of time, your brain encodes and "wires" this neurologically as pain--sometimes even after the actual physical injury has long since healed.
This is one basis for why and how injuries occur.
Two ways that effective physical therapy addresses this is:
1) Familiarize the individual with an assortment of movements to decrease the risks that unfamiliar situations place upon the human body.
2) Increase the durability or capacity of tissues to withstand considerable forces, decreasing the chance of injury.
(Video is from Bill Hartman of IFAST University, LLC)