"Solus eris" is a philosophical and scientific treatise by the Hungarian philosopher Zoltan Ambruš. In the book, the author considers the concepts of loneliness, existence and individuality in the context of the modern world. Using deep research in the field of philosophy and psychology, Ambrush forces the reader to rethink his attitude to his own "I" and his place in society. "Solus eris" is a thought-provoking book that inspires self-discovery and encourages the search for deep truths.