One of the themes in "The fault in our stars" is that even though  everyone is going to die someday you never know what will happen beyond death. It's like Augustus's and Hazel's fear of oblivion.The Main characters in this book are all faced with a serious disease that faces them to look at the possibility of their death, Unlike how the healthy people. In the beginning of the book Hazel points out in support group that everyone will die eventually so they might as well question what might happen after death and that all that is to come up soon is oblivion. Also at this support group Patrick asks Augustus what is his biggest fear and he says "Oblivion." That's when Hazel and Augustus found something they both had in common for the first time. Hazel believes that since there was a time before humanity that there will also be a time after. This theme goes on throughout the whole novel.