Full Idea
Socrates thought it a shocking idea that when a man actually has knowledge in him something else should overmaster it, ..but this is glaringly inconsistent with the observed facts.
Clarification
'akrasia' is weakness of will (incontinence, lack of control)
Gist of Idea
Socrates was shocked by the idea of akrasia, but observation shows that it happens
Source
comment on Socrates (reports of career [c.420 BCE]) by Aristotle - Nicomachean Ethics 1145b24
Book Reference
Aristotle: 'Ethics (Nicomachean)', ed/tr. ThomsonJ A K/TredennickH [Penguin 1976], p.228
A Reaction
Aristotle seems very confident, but it is not at all clear (even to the agent) what is going on when apparent weakness of will occurs (e.g. breaking a diet). What exactly does the agent believe at the moment of weakness?