Werther and Victor both behave in ways that appear self-destructive. What causes them to behave in this way?

Werther, the protagonist of Goethe's epistolary novel The Sorrows of Young Werther, and Victor Frankenstein, the protagonist of Shelley's Frankenstein, share similar personality characteristics. For example, they are both intensely passionate and self-obsessed, qualities that lead to their self-destructive ways.
Though Werther's passion is directed toward a love object, Lotte, and Victor's passion is directed toward his ambition to create life, the two men behave similarly. Before Werther and Victor become obsessed—one with a woman and the other with his work—both men seek isolation. In this state of isolation, with no one to check their emotions and behaviors, they find their self-destructive tendencies strengthening.
When Werther meets Lotte and discovers that she is unattainable, he reacts to his predicament in a manner similar to Victor's reaction to the challenges of creating his creature. Neither man is able to calm himself and hear reason, so they both succumb to their intense emotions. Werther and Victor both experience a sense of torment, thanks to their sensitive personalities.
Werther demonstrates his self-destructive tendencies most dramatically when he kills himself, while Victor Frankenstein's self-destructiveness manifests in his ambition and single-mindedness in pursuit of his creature's birth and then its death. Though Werther and Victor lead vastly different lives, their self-destructiveness comes from the same source: themselves.