An actor must make his needs (goals, wants, objectives) so strong that he is willing to interfere with the other actor in order to get what he needs. Interfering means getting in their way so that what you want is stronger than what they want.
Michael ShurtleffAn expression of feeling isn't worth anything unless it interferes with what the other actor in the scene wants.
Michael ShurtleffCompetition [in a scene] is healthy. Competition is life. Yet most actors refuse to acknowledge this. They don't want to compete. They want to get along. And they are therefore not first-rate actors.
Michael Shurtleff