Endometriosis is a tough one. It presents as abdominal cramping pain, which literally a million things can present as that. The only way to diagnose it is via direct visualization, AKA surgery. I'm not a surgeon, but it's a good idea to avoid surgery if at all possible. Even the most successful uncomplicated surgery can cause lifelong problems with adhesions and obstructions. A surgical complication could be as severe as death.
If we could have a diagnostic tool that is reliable and noninvasive, that would be wonderful. But it currently doesn't exist.