Our gadgets are getting smarter. Technology can log what we buy, customize what we consume and enable us to save and share every aspect of our existence. In the future, we're told, it will even make public life - from how we're governed to how we record crime - better. But can the digital age fix everything? Should it? By quantifying our behaviour, Evgeny Morozov argues, we are profoundly reshaping society - and risk losing the opacity and imperfection that make us human.