a jack of all trades and a master of none

A jack of all trades and a master of none is a figure of speech referring to someone that is competent at many things but isnt outstanding or perfect at any of them. Jack of all trades is a cliche used for someone skilled at many things, so when they are not a master of one, they may be moderately skilled at many different things, but they are not a master, or professional, at any of them.