While pursuing "higher, faster, stronger" digital technology advancements today, the survival and development patterns of individuals, society, the environment, and the world are increasingly under pressure and overdrawn — approaching the brink of unsustainability. Faced with this structural issue in the relationship between humans and technology, incremental innovations that follow traditional lines of thinking are no longer sufficient to address the root of the problem or reverse the trend. Instead, a set of macro−level theoretical frameworks is needed for attribution, explanation, and resolution. From the "Biophysics−Intellect−Xin" perspective of Human−Engaged Computing, we argue that the root of current unsustainable situations lies in the unsustainability of the human "Xin". Past human−machine relationships, focused on building knowledge repositories ("Intellect") and satisfying physical needs ("Biophysics"), not only fail to address today's sustainability challenges but also exacerbate real−world problems through overdevelopment. Accordingly, a potential solution lies in deriving a top−level design from a human−machine relationship centered on "Xin". This approach would meet human material needs while restructuring the underlying mechanisms and environment of digital technology to foster peace in "Xin", thus gradually promoting the long−term sustainable development of individuals, society, the environment, and the world.