What works in the script can't always work in practice. It's entirely usual for directors to cut whole characters from their film in the edit, for the sake of brevity or just because said characters' scenes weren't working in the execution. This means actors can unwittingly find themselves on the cutting room floor, regardless of talent or of effort put in. Pity, for one, poor Michelle Monaghan, the True Detective star who was cut completely from both Syriana and Constantine. There have been instances where the biggest stars have seen their work edged out of films for one reason or another, even if it seems commercially counter-intuitive to cut a major star from a feature. Big names equal bigger business; which is why, for example, Gwyneth Paltrow got paid $3.6 million to have her name appear prominently on the poster for Infamous even though she appears in just one scene of the movie. It should be noted too that studios generally don't want to waste the time of A-list movie stars or offend them by cutting the hard work they put into a film. With that said, sometimes directors choose the integrity of their film over potential profits or actors' egos. And when they've gotta go, they've gotta go.