Sentence:  "Strickland's painting in my studio." / "Well?" / ... / "Strickland can't work with anyone else in the studio." / "Damn it all, it's your studio. That's his <WSD>lookout</WSD>." 
Meaning of the word marked with <WSD> tags:  One's perspective, outlook; hence, one's responsibility. "(used with a possessive pronoun or a noun in a possessive form)".