What casting of actors means in cinema

It’s note worthy that a film like Godfather would not have been effective if it had missed on casting Al Pacino, or recently the Wolf of Wall Street had missed on Leonardo Dicaprio.

Whats important is that a good actor would be very effective regardless what role is played, even if typed cast or unduly cast, but the point being discussed here is that in the cinema casting can change the game.

It does not necessarily get restricted to main actors or star being cast. A powerful cinema would be only effective and yet powerful only if the casting is taken to be as a whole.

That means when a casting director cast actors in the film the entire cast have to complement each other and the casting has to be in totality and not in patches of only main actors.

If pick up any effective powerful cinema from any where in the world cinema, one would find that each and every human appeared in the film would complement each other even if they are not sharing the same frame of the camera.

If this is not true, then why best of films when made with best of actors often go flop, be it Hollywood or Bollywood or any other wood.

Readers do suggest me of good films from international cinema.