Two novels that have very comparable themes are: Flowers For Algernon, by Daniel Keyes and The Notebook, by Nicholas Sparks. Both have many comparable situations and themes, even though both books are different in many ways.
The Notebook, is a romantic love story that some might call a tragedy. It's the story of a 31 year-old man named Noah, and a 29 year-old woman named, Allie. They both meet each other as teenagers, and for a summer they fall in love. They are separated for 14 years and they both have trouble forgetting the magical summer they shared together. One day, Allie unexpectedly shows up in Noah's life, three weeks before she is to marry her fiancé. Noah and Allie wind up together, and grow old with one another. They are together for many years before Allie ultimately becomes senile with old age. .
Flowers For Algernon, is the story of a 32 year-old, mentally retarded man named, named Charlie. Charlie is recommended by his teacher, Alice, for a scientific experiment in which he will become more intelligent. The test works and Charlie becomes a genius. He learns of his memories of his past, and he feels love and emotions that he has never felt before. He has a hard time coming to his self realization. When he becomes intelligent, he discovers that there is a flaw in the test and that he will again become mentally retarded. He has a companion, a mouse named Algernon. Algernon is also subject to the same test. The book ultimately ends with Charlie checking himself into a home because he is fearful of his retarded self and the death of Algernon.
A common theme shared in these two novels, is the theme of how memories affect the present. In Flowers for Algernon, Charlie becomes intelligent and he is mindful of his thoughts, and memories of the past. He remembers his mother, who abused him mentally, and traumatized him into being afraid of having sexual thoughts when he was younger.