How can we hope to detect and eliminate error?

"The question about the sources of our knowledge . . . has always been asked in the spirit of : ‘What are the best sources of our knowledge – the most reliable ones, those which will not lead us into error, and those to which we can and must turn , in case of doubt , as the last court of appeal ?’ I propose to assume, instead, that no such ideal sources exist – no more than ideal rulers – and that all ‘ sources’ are liable to lead us into error at times. And I propose to replace, therefore, the question of the sources of our knowledge by the entirely different question : ‘ How can we hope to detect and eliminate error?’
Karl Popper - ‘ Knowledge without Authority ’ (1960)"