The human body is an amazing machine.
It is a big pulley system that all works together. Everything is connected. I am frequently amazed at how complex a machine the human body is.
Just as the flap of a butterflies wings on one side of the world can cause a tsunami on the other side of the world, a small muscle imbalance in one area of the body can cause immense pain and discomfort in another area of the body.
This is very accurate with knee pain. Most knee pain involves an imbalance of the muscles in the hip, caused by muscle spasm. Whether that muscle spasm in the hip causes the knee pain, or is from compensation for the knee pain, can be hard to say.