I think good actors can sort of see into people and immediately you have a chemistry with them or not. It's like an affair with no mess. You don't actually consummate it, but you get to pretend, imagine what it would be like. ↗
I have directed good actors and have gone through the process which is more detailed in theater in a way. You have to get people to stay for two or three hours in a performance. They need more talk and rehearsal than in films. ↗