Sir Alec Guinness had to have had his patience tested to the limit with his 'blind butler' character name of Jamesir Bensonmum. This movie dialogue scene by itself provides the explanation.
On serious side, Sir Alec Guinness performance in this film should have earned him a Best supporting actor Oscar nomination even if he wouldn't have won the category. Alec's ability to change character personalities near the movie climax itself is what should have earned him a nomination alone.
Peter Sellers also did well, but Alec stole the show.