Ok, my interpretation of that idiom is that 'not all efforts produce a result' - not all flour will turn into bread, but some will
well , that saying is rather precise. I mean it refers to a specify issue from a point of view of a saying-user(sic). It doesn't generalizes like most of saying.
Such and such thingy not gonna work - says A or he can say - insert saying - that. Makes him look sage and savvy rather than a gossiping bitter fart that he is. lol
Besides that saying is not oft used nor popular. Its alive to some extent due to literature. I'm sure there are any people in Poland that never heard it.