BCI holds a high, and perhaps bold, promise: human augmentation through the acquisition of new brain capabilities that will allow us to communicate and interact with our environment directly by 'thinking’. This is particularly relevant for physically-disabled people, but is not limited to this population. Yet, how is it possible to fulfil this dream using a 'noisy channel' like brain signals? In this talk I will argue that, despite the quality of the brain signals that we can monitor, truly operational brain-computer interaction is embedded in a more complex system. I will put forward four principles to design such brain-controlled devices, which I will illustrate through working prototypes of brain-controlled robots and applications for disabled and able-bodied people alike.