Direction and editing is responsible for almost everything about a performance. My goto example is in Raiders of the Lost Ark there is a monkey. That monkey has lots of screen time. He hits his marks, says his lines, and even has a dramatic death scene. Now does that monkey deserve an oscar or do you think maybe the monkey's handlers were involved at some point? Actors are not so different from this monkey. If they're not giving you what you want then you need to try again until they do. If they can't do what you want, you need to edit around it.

Another example is Terminator 2. The entirety of John Connor's (Edward Furlong's) dialog was redubbed by another actor. Allegedly this was due to his voice changing during production, but I suspect it could have been because of performance weakness. The redub was expensive and hurt feelings, but it was what needed to be done. The movie is still a classic.

Compare that to The Phantom Menace where every moment of a child actor being on screen is pure suffering. At this point there's a cottage industry of pointing out the directorial failures of George Lucas so I don't think I need to go into it, but the contrast is stark.

Direction and editing is responsible for almost everything about a performance. My goto example is in Raiders of the Lost Ark there is a monkey. That monkey has lots of screen time. He hits his marks, says his lines, and even has a dramatic death scene. Now does that monkey deserve an oscar or do you think maybe the monkey's handlers were involved at some point? Actors are not so different from this monkey. If they're not giving you what you want then you need to try again until they do. If they can't do what you want, you need to edit around it.

Another example I use is Terminator 2. The entirety of John Connor's (Edward Furlong's) dialog was redubbed by another actor. Allegedly this was due to his voice changing during production, but I suspect it could have been because of performance weakness. The redub was expensive and hurt feelings, but it was what needed to be done. The movie is still a classic.

Compare that to The Phantom Menace where every moment of a child actor being on screen is pure suffering. At this point there's a cottage industry of pointing out the directorial failures of George Lucas so I don't think I need to go into it, but the contrast is stark.