Recent behavioural research has debunked the idea of humans as entirely rational. This paper suggests the gap between human behaviour and human cognition can in fact be explained not necessarily by irrationality but by: performance errors; computational limitations; the wrong norm being applied by the experimenter; and/or a different construal of the task by the subject. The authors re-run common experiments demonstrating behavioural biases and find computational limitations in particular underlie seemingly irrational responses to several experiments.