It is more critical for theater actors to have their lines firmly memorized because their performances are going to be live.  With a TV or film actor, for the most part, they can ask for the line and retake the shot.  There are a few live television shows but for the most part, things are recorded so while it is important for film actors, it is imperative for theater actors.
        
             
        
        
        
I can’t draw very good my art is only good when i’m high
        
             
        
        
        
St. Christopher, patron saint of travelers