Asimov isn't simply declaring that writing matters to him—he's suggesting that the act itself, the doing, has become fused with his existence in a way that makes the distinction between hobby and necessity collapse entirely. Most people talk about passion as something they *pursue*, but here the writer describes it as something he cannot *stop*, which reverses our usual understanding of motivation. When a surgeon or teacher says something similar about their work, we recognize the particular exhaustion in it: not the pleasant burn of dedication, but the literal inability to exist otherwise. That's the difference between loving what you do and being unable to imagine yourself as a self that doesn't do it.