I say to myself, 'I don't know how to act - and why does anybody want to look at me on-screen anymore?' ... Lots of actors feel that way. What gives you strength is also your weakness - your raging insecurity.
The key to every actor is deep, deep insecurity.
In other characters, it's driven by insecurity, or it's driven by fear, or - there's always a driver. And all the physical manifestations, you need your way in.