That's what actors are trained to do. If you need an actor to, let's say pretend that the love of their life just died, like in John Wick.... just tell the actor to think back to a time when the love of their life died- oh that's right, Keanu Reeves' love-of-his-life died tragically and he's never really moved on as far as anyone knows. He wasn't acting then- he was just recalling the pain, the agony of that loss. The grief, everything you see on his face is *real.* It may not be as fresh as it is for the character known as John Wick, but just throw in some dramatic lighting, music, and camerawork... and you have a believable scene. Also, give him a dog and then have the bad guy kill it. That's a 100% surefire way to get an audience to fall in love with the protagonist, regardless of how horrible he is, and the audience will *despise* the villain with a passion unlike anything that, say, the murder of the protagonist's daughter or something. People are weird like that. Some actors suck at acting though, and can't dredge up heavy emotions. I think a lot of them are numb to it, because of the horrible shit they are subjected to in order to become "part of the club". When they need Leonardo DiCaprio to act angry as fuck, maybe he just has to think back to being raped by people like Weinstein? Does that work anymore after he's re-enacted his own abuse on a new victim? Who knows. I've heard of some actors requiring physical injury in order to produce tears for a crying scene- can't remember who it was, I think it was a woman, she would have someone jab her in the foot with a needle before her big crying scenes.