"Yeah, I think the common denominator - and this is probably going to sound like Acting 101 - but the common denominator is belief in the character in the moment"

Jenna Elfman is suggesting that the secret to effective acting is to think in the character you are playing. This indicates that the actor must be able to suspend their shock and become the character they are playing. This is a basic principle of acting, and it is important for an actor to be able to do this in order to succeed. It is inadequate to simply remember lines and recite them, however rather the star must have the ability to embody the character and make the audience think in them. This is why it is so crucial for an actor to be able to think in the character they are playing in the minute. It is this belief that will make the audience think in the character and the story being told.