Why did Graham Greene call an autobiography “a sort of life”?

Graham Greene used the phrase “a sort of life” as the title for his 1971 autobiography to reflect the inherent limitations of the biography genre when applied to oneself.12

He argued that an autobiography offers a specific type of biographical truth that is inevitably reshaped by the author's recollection. Because memory is plastic, the narrative is subject to both conscious and unconscious omissions and distortions. Consequently, Greene believed that such a work cannot capture a life in its entirety, but rather presents a version of what the subject is impelled or chooses to reveal at a particular moment in time.12