Artificial intelligence has already entered our lives. While we enjoy the convenience it brings us, we are also worried that it might take our jobs, access our data, and make decisions for us. Given the numerous challenges we will be facing in the future, how do we make sure we can stay at the forefront of time and survive? Following Sapiens: A Brief History of Humankind and Homo Deus: A Brief History of Tomorrow, as the finale of the trilogy, the book 21 Lessons for the 21^st Century will bring you to a significant discussion about human destiny in the twenty-first century.