how would one measure ones' incompetence ? how would one rate their vision in comparison to others ? 

it's given that dunning-kruger works against one in this endeavour. to begin with, let's assume there's no way to measure and assign a static number to this quality of ourself. 

guy-ritchie-jason-statham throws us a bone here - you get better by playing a better opponent[1] 

so unless your playing, and getting better, it's not possible to know how incompetent you are . and this information is very limited. it only tells you how bad you are compared to the last game you lost, it shows you only the next hill to climb, not the whole range . 

most of us begin by seeing a tiny slope that hides the foothills of the Himalayas, then, climbing up and down a staircase in our house, we are assured that we can climb that hill, and therefore master the skill soon, maybe tomorrow. leaving home and testing ourselves only brings pain at first. 

Having climbed a few hills and having reached a mental state where one does not panic after seeing the full range laid out in front of us, is the best steady state one can aim for - the plateau of skill that one keeps trudging - content that what lies ahead is not a given defeat, and that our past victories are not trivially achieved by others ...

[1] Revolver