Theatetus by Plato (369 BCE)

Socrates believes that knowledge is innate in man, but that man does not always allow knowledge to rule him.  Emotions play a role and they can at times overwhelm knowledge.  Socrates asserts that man knows the right thing to do, but does not always choose to act that way.  Socrates warns the reader that what is good and virtuous is complicated.  He rejects the notion that a certain amount of bad behavior can be outweighed by good behavior.  The virtuous behavior does not negate the bad behavior.
    Socrates states that all desire is for pleasure and nothing else.  Man seeks happiness, even though what brings him happiness is not always good.  This premise is necessary because without it there is not an explanation for why man does things that are not virtuous.   The desire to do something outweighs the negative impact the behavior will have on your relationship with your parents, which is a virtuous relationship.
Socrates premise that mans desire for a course of action is in direct proportion to the amount of pleasure he will receive.  This explains why man would seek pleasure in the short run, because it is an intense and overwhelming emotion that can interfere with man’s pursuit of what is virtuous, even of he has the knowledge of it.  For example, man has the knowledge that marital fidelity is virtuous and will bring both he and his spouse happiness.  Occasionally man is tempted to have sex with someone who is not his spouse.  He is driven by the desire for immediate pleasure, and may not consider the consequences for his long-term happiness in the pursuit of his immediate desire.  If he chooses to have an extramarital affair, the pain that he endures later outweighs the pleasure he enjoys in the moment.
Socrates argues that when man demonstrates a weakness of will, what is really happening is that he has not correctly assessed the damage that his pursuit of pleasure will have or that he has incorrectly assessed the amount of pain that he will endure based on his action.  Socrates believes that if man was able to accurately measure pleasure and pain, and the consequences of them he would always act in a knowledgeable way.  When man makes the wrong assessment, he errs.  This can appear to be a weakness of will, but it is actually a failure of knowledge.  I agree with Socrates in principle.  For example, a robber chooses to hold up a liquor store to steal money for his own pleasure.  He is aware of the fact that what he is doing is illegal and that he could go to jail if he is caught.  Often the thief makes an inaccurate assessment of his risk of being caught.  He is conscious of the bad possibilities that he faces with his action, but he makes the mistake of believing that he will not be caught.  His emotions overrule his knowledge, and lead to his weakness of will.