The importance of reputation is the first of two central themes in Thirteen Reasons Why. Hannah traces the beginning of the end for her to Justin, the boy with whom she shared her first kiss. Their kiss was chaste and innocent, but in Justin's mind, it became something more, and he began to brag. As Hannah accurately puts it:

a rumor based on a kiss started a reputation that other people believed in and reacted to...(creating) a snowball effect.

As Clay realizes when he listens to the tapes, "(Hannah's) reputation started in Justin Foley's imagination," and because Justin sets the precedent with his gossip, a second incident occurs that is even more damaging than the first. His attention having been drawn to Hannah as a sex object, Alex, who had been her friend, lists Hannah as "Best Ass in the Freshman Class," unintentionally but irrevocably changing the way people perceive her, and making her life a living hell. Hannah above all yearns to establish meaningful relationships with others, but individuals like Clay who might have made a difference in her life stay away because they are afraid of her reputation. Instead, Hannah is continually approached by boys who have only one thing on their minds, and the constant harassment soon renders Hannah unable to trust anyone, further increasing her isolation. After being objectified and betrayed time after time, Hannah, completely beaten, finally allows herself to succumb to the reputation set for her, and follows this capitulation by taking her own life.

A second theme examined in the book, a theme which is closely related to the first, is the issue of responsibility. Very few of the characters actually set out to hurt Hannah, but because they give little thought to the significance of their actions, they end up playing a part in the total destruction of her life. Hannah addresses this fact up front, telling her listeners:

I know you didn't mean to let me down. In fact, most of you listening probably had no idea what you were truly doing.

The point Hannah wants to make on her tapes is that, even though an individual's actions might seem insignificant, "in the end, everything matters." Alex, for example, was only trying to get a laugh, and perhaps to get back at Jessica for breaking up with him, when he created his "Best Ass" rankings; he certainly never intended to ruin Hannah's life by naming her first on the list. The fact that the resulting events were not instigated on purpose does not absolve Alex from guilt, however. Hannah succinctly states:

when you hold people up for ridicule, you have to take responsibility when other people act on it.

As Hannah stresses the importance of an individual's seemingly inconsequential deeds, she emphasizes the interconnectedness of all actions, because "everything affects everything." The indignity and torment she endures is no less devastating due to the fact that it is most often "just an aftereffect of someone else's callousness," and she reiterates that "when you mess with one part of a person's life, you're messing with their entire life." Hannah's bitter narrative is a testimony to the effects of failed responsiblilty; because of the thoughtless acts of a host of individuals, a false and unendurable reputation was created for her, and though any one of them might have saved her, no one cared enough or was perceptive enough to understand her situation, and take responsibility and intervene.

It is clearly a dark world that Hannah inhabits, and in her recordings she exposes the depravities that afflict humankind, another theme that is explored in the narrative. In a starkly realistic landscape where drinking and sex are the primary weekend activities for a large number of teenagers, drunken boys pummel each other to maintain an image of toughness while "wall(s) of people...four bodies deep" voyeuristically look on with excitement, and students looking out exclusively for their own interests commit the small cruelties that ruin each others' lives. Hannah acknowledges that she too is complicit in creating an environment where individuals are often blind to the consequences of their actions and lack the resolve to put the needs of others first if it involves venturing out of their own comfort zones. Like the people she accuses of not caring enough, Hannah cannot find the strength to act when she could have prevented what turned out to be a fatal car accident or to step forth when she could have stopped Bryce from raping an unconscious girl. Hannah owns, with unqualified humility, that in the final analysis, she is no better than those who made her life so miserable, and this knowledge only contributes to her ultimate despair. Despite what anyone else has done to her, when all is said and done, Hannah, flawed like all the others, admits, "it all ends with—me...me...giving up...on me."