The Socratic Paradox: People act immorally, but they do not do so deliberately.
Everyone seeks what is most serviceable to oneself or what is in one's own self-interest.
If one [practically] knows what is good, one will always act in such manner as to achieve it. (Otherwise, one does not know or only knows in a theoretical fashion.)
If one acts in a manner not conducive to ones good, then that person must have been mistaken (i.e., that person lacks the knowledge of how to obtain what was serviceable in that instance).
If one acts with knowledge then one will obtain that which is serviceable to oneself or that which is in ones self-interest.
Thus, for Socrates…
knowledge = [def.] virtue, good, arete
ignorance = [def.] bad, evil, not useful
Since no one knowingly harms himself, if harm comes to that person, then that person must have acted in ignorance.
Consequently, it would seem to follow we are responsible for what we know or for that matter what we do not know. So, then, one is responsible for ones own happiness.
The essential aspect of understanding the Paradox is to realize that Socrates is referring to the good of the soul in terms of knowledge and doing what's right— not to wealth or freedom from physical pain. The latter play no role in the soul being centered.