Gatsby replies that of course you can repeat the past. In fact, that belief has laid the foundation of his whole life for the past five years as he amassed the fortune that he believes now exceeds Tom Buchanan's. The money is necessary to attract Daisy, who Gatsby believes will now leave Tom for him.
Gatsby is confident that he repeat the past when he and Daisy first met. This time around, however, she will be his because he now has enough money. His simplistic view reveals how completely he has skewed reality in his desperation to have the woman of his dreams.
Gatsby's response to Nick's observation that you can't repeat the past is incredulity. He says, "Can't repeat the past? Why of course you can!" To him, it seems perfectly reasonable to expect that Daisy would be able to tell Tom that she never loved him, and pick up where she left off with him, Gatsby, five years ago. Gatsby is determined to "fix everything just the way it was before". As he talks, Nick understands that in actuality, Gatsby wants to recover more than just Daisy. He is looking for "something, some idea of himself perhaps, that had gone into loving Daisy". His life has been incomplete since he lost her, and he somehow feels that if he could just go back and do it all again the right way, he would find the thing that he has been missing (Chapter VI).
He says "Can't repeat the past? Why, of course you can!"
This iconic line reveals Gatsby's obsession with the past. He wants to have this old life with Daisy. He wants things to return to the way they were before the war. Gatsby is so fixated on the past that he fails to see the present and anticipate the future.
To downhillrider, I think that you have not yet reached the level to appreciate a literary work. Who said that Fitzgerald's masterpiece is pointless?
Gatsby says "'Can't repeat the past?' he cried incredulously. 'Why of course you can!'" pg 111 of the penguin edition this is because he wants to recreate his relationship with daisy and so says this as he doesnt like this idea or dream (remember american dream is a key theme) being challenged
hope that helps
The great gatsby is a pointless book and should never be read!