master of nothing expression

There is this expression, …?, master of nothing, where the ? marl is some short expression equating to knowing a lot about things, but then, being less than a master at those things, anyone know, google helped little in this broad area…thanks

Jack of all trades, master of none?

Well, I sort of lost you in your question, but were you referring to the phrase “Jack of all trades, master of none”?

And on preview Rasa offers the same explanation.