Remember in grade school in art class you'd get strands of glue binding your fingers together. These would be in theory similar to filmy adhesions but instead of holding yr. As time passes these adhesions grow more and more dense. In addition to pain adhesions can cause rare but serious complications if they cause blockages in the digestive or the urinary tracts. Since adhesions can affect the placement of the tubes and ovaries it is harder for an egg, once ovulated to make its way to be fertilized.
Adhesions can also cause blockages in the tubes themselves.
Finally, women with Endo. tend to have a lower ovarian reserve than usual for their age. In short this means they run out of good quality eggs while still in their prime reproductive years. The only way to diagnose Endo. Whereby a camera is inserted thru a small incision in the belly button and the disease and its effects can be directly viewed. No one knows what causes Endo.