What does the quote 'to know that you do not know is the best.To pretend to know when you do not is a disease' mean?

The quotation, 'To know that you do not know is the best. To pretend to know when you do not is a disease,' expresses a classical sentiment that can be explained as follows: Truth, insight, and wisdom, even health and happiness (or, all that is the 'best'), follow from genuine knowledge. Thus, to know that one does not know is a step towards all that is 'best' for oneself. Moreover, pretending that one does not know must be a step away from it: this, for the source of the quotation and also in the classical tradition, is one of the worst afflictions (it is even a 'disease') of humankind.