A forehead that's narrow in relation to the height of the face shows you are cautious about putting yourself out there without knowing your subject well. You gain confidence through knowledge and experience. If say say you know something, chances are very good that you really do. You work hard to gain the knowledge so you can feel reasonably confident in matters and will readily admit it when you don't know something. You are a specialist, learning your subject in depth, rather than a generalist.
