Herzog by Saul Bellow

The novel centers around Moses Herzog, a middle-aged, intelligent yet distressed man who is going through a mid-life crisis. After his second marriage fails, he falls into a state of emotional turmoil and begins writing letters to friends, family, and even famous figures, expressing his philosophical thoughts and personal feelings. His journey of self-discovery and understanding forms the crux of the story. It's a profound exploration of a man's struggle with the complexities of life and his quest for meaning.

The 169th greatest book of all time