Your description of this theme in sci fi reminds me of a Brandon Sanderson book that I've been thinking of reading, Legion.

"Stephen Leeds, AKA “Legion,” is a man whose unique mental condition allows him to generate a multitude of personae: hallucinatory entities with a wide variety of personal characteristics and a vast array of highly specialized skills. As the story begins, Leeds and his “aspects” are drawn into the search for the missing Balubal Razon..." http://brandonsanderson.com/books/legion/legion/