This is not something merely “commonly accepted in yeshivas,” but Jewish law codified in the Shulchan Arukh, originating in the medieval authorities (Rishonim). See Shulchan Arukh, Yoreh De’ah, section 98: a doubt that stems from lack of knowledge is not considered a doubt, and therefore cannot be used to permit something. [A basic example: an olive-sized amount of meat fell into a pot of milk, and I don’t know how to calculate the amount of milk in the pot to determine whether it is sixty times the meat. The doubt here is neither a legal doubt nor a factual doubt, but rather stems from my lack of knowledge of the calculation.]