What led to Dr Jekyll's "profound duplicity of life"?

Jekyll maintained social respect while keeping his more questionable vices secret. When he reached adulthood, Jekyll found that he was living two lives, one of the utmost respectability and social graces, and the other of hidden pleasures and dark underpinnings. As a scientist, Jekyll decided to examine the dual nature of man through mystical study that Lanyon found particularly offensive. In the latter, Jekyll insists, "man is not truly one, but truly two," and he explains how through his research he hoped to separate each side.