This Spanish saying corresponds to the English one that says “In the land of the blind, the one-eyed man is king” and refers to people who stand out from others, that is, those people who do not have great talents but are less mediocre than others. In short it refers to what seems good among the bad.
For example, if in a group all the people do not have money, the one who has it will be the most renowned for the simple fact that he/she has at least something. Therefore, in the literal sense of the proverb, where everyone is blind, the one-eyed man is a king, because at least he has the joy of seeing with one eye, compared to whom can’t see anything.
In a context marked by the mediocrity of people, the king is someone who in his/her mediocrity for some reason is in a superior position within a group of people with even lower capabilities.