Have you ever been told you over-pronate, or your arch collapses when you run? If so, you'll want to take a look at this video.
What could the ankle have to do with over-pronation and what does that have to do with knee pain? This video will help you understand why an orthotic might not always be the best solution for a collapsing arch and why it could lead to knee pain.
In some cases an orthotic can be a great solution to the problem. However, the only way to know if that's the right solution for you is to take a look at the whole picture.