This one from the Endometriosis Foundation of America:
Any amount of endometriosis can cause pain, and the disease does not need to be advanced to cause significant symptoms.
That is in no small part because, at least in the US, the most common method of determining staging looks like this:
To be fair, this system’s intent is to determine staging with respect to infertility. So, endo staging doesn’t measure pain because the endo staging system was never designed to measure pain.