Gatsby's disillusionment is highlighted in this quote. He is so invested in his idealisation of Daisy that he believes he can achieve the impossible. He can't turn back time to 5 years ago but he also can't accept that Daisy is a different person now, with a different life, husband and child. This highlights the futility of 'American Dream' as well as illusion versus reality as Gatsby's illusion is fought by Nick who sees the reality.