Short answers, pulled from the story.
Guilt is a moral emotion that occurs when a person believes, accurately or not, that they have compromised their own standards of conduct or violated universal moral standards and bear significant responsibility for it. Understood as a collection of basic emotions, it is composed of self-directed anger, sadness for the victim, anxiety, and fear. It is closely related to remorse, regret, and shame.
Guilt is conjured internally when one's personal morals are violated and focuses on the thing done, while shame results from violating cultural or social values and focuses on the self as a whole. Ruth Benedict framed shame as arising from a real or imagined negative perception coming from others. Helen Block Lewis noted that in guilt the self stays unified, while in shame the self is split.
Individuals high in psychopathy lack any true sense of guilt or remorse, and instead rationalize their behavior, blame others, or deny it. Psychologists attribute this to a lack of moral reasoning, an inability to evaluate situations in a moral framework, and an inability to form emotional bonds due to a lack of empathy. One study found psychopaths could switch empathy on at will when instructed to.
Sigmund Freud attributed guilt to the conscience, which he called the superego, rather than to God. He blamed it on the individual's own fear of loss of love and relationships, beginning in childhood with a fear that parents could reject the child, a fear the child turns inward to create self-directed anger.
Guilt proneness is a personality trait reflecting a tendency to feel negative emotions about one's own misdeeds even when others do not know about them. The strong sense of responsibility in guilt-prone people makes them trustworthy, and the trait is reliably associated with moral character. Feelings of guilt can also prompt virtuous behavior such as restraint and less prejudice.
Collective guilt is the unpleasant and often emotional reaction among a group of individuals when it is perceived that the group illegitimately harmed members of another group. It often results from sharing a social identity with others whose actions threaten the positivity of that identity, and it requires the individual to identify as part of the in-group.
The word guilt developed from the Old English form gylt, meaning crime, sin, fault, fine, or debt, which is possibly derived from the Old English gieldan, meaning to pay for or debt. Its development into a sense of guilt is recorded in 1690, and the phrase guilt by association was first recorded in 1941.