Why did Septimus Warren Smith commit suicide?
Septimus Smith is a sensitive young man who fought in World War I. As a result of that experience, he has PTSD, or, as it was then called, shell shock. He experiences delusional and suicidal thoughts that frighten his wife. He can't shake his memories of Evans, his friend who died in the war.
As Mrs. Dalloway is preparing for her grand party, Lucrezia, Smith's wife, is trying to arrange for doctors to help Septimus. Both Dr. Holmes and the important mental health specialist, Sir William Bradshaw, are insensitive to Smith's real needs. Bradshaw wants to shut him away in an asylum. Bradshaw cares more about his career ambitions than his patients.
To avoid his doctors and because he can't bear life any longer, Smith jumps out a window and dies. This makes Bradshaw late for Mrs. Dalloway's party. When Mrs. Dalloway hears the news of the suicide, she feels a shock.
Some critics have contended that Bradshaw is a portrait and indictment of insensitive society doctors who treated Virginia Woolf for mental illness. Woolf seems to be communicating in the novel that death is preferable to their "cures."
Septimus returned from the war with shell-shock and had delusional thoughts and hallucinations. His mental disorder was not well diagnosed, and ultimately he killed himself rather then bear the pain of his mental disease.
septimus killed himself because this was the only way in which he could preserve his soul from being succumbed by society. he knew he couldn't find his place in the world anymore, so he commited suicide.