ON ACTING: The Opinionated Actor
But...because all opinions by definition fall short of absolute truth, that should be no reason for the speaker to feel uncertain; or worse, feel that they should apologize for those opinions (words of dialogue).
NOBODY knows the truth...so, since nobody knows the truth, since you don't know the truth any better than I, my opinion is as good as yours; unless and until you convince me of the opposite,
So in terms of acting, a well acted, interesting scene is a fair, open and honest battle of opinions (dialogue). No more, no less. And good actors regale in giving as good as they get.
Bad actors, on the other hand, often seem angry, frustrated, moan-y or whiny when forced to give an opinion in order to secure the victory, or concurrence. Perhaps they act in those ways because they don't believe in their inherent right to be right, to their own opinion. They therefore don't find any joy in the tactical struggle of their logic vis-a-vis the other character.
Almost unfailingly the attitude of the uncomfortable-actor-in-conflict, as manifested in body and voice, betrays their dislike of the logical give-and-take. Those manifestation(s) of their discomfort makes the audience uncomfortable...which causes the audience (and similarly casting directors who often witness such performances) to find such actors exhibiting those traits off-putting and unappealing.
To such unappealing actors, those who find conflict and the battle of opinions lacking in pleasure and delight, I offer this suggestion. Learn to play the game ping pong; and learn to play the game human/dialogue ping-pong from it. Because that is what the dialogue in a scene is: a game of verbal ping-pong. The actors are the paddles in the scene, and their respective thought, as it is expressed in the dialogue, is the ping-pong ball, to be hit back and forth in a wide array of shots, some twisting, some hard, some with lots of spin, some tantalizing soft, perhaps even with backward spin, some not hit as a winning shot, but as a set-up for the following winning shot.
Actors: learn to enjoy the game of life; to have fun batting it back and forth. Remember, it is a game; a game of wits and wants and "believe me and agree with me or I'll keep battling with you forever." There is nothing about the game to get necessarily angry, or frustrated, or moan-y or whiny about. Conflictual tactics is life. We all are destined to play it. The only choice to be made is whether to play it gleefully or with chagrin. "It is not whether we win or lose, but how well we play the game; as in life, it is not the ecstasy of the victory or the agony of defeat, but the joy of the struggle." Such is life; such is good acting.