Wanda stared at the Doctor in surprise at his question and shook her head with a half shrug. "No, I haven't wondered. I thought it was obvious. Unless- it isn't?" She stared at him for a moment, uncertain, and then continued with an explanation. "If Billy was created by me- well, not me but, you know- anyway, if his existence, or at least his power, is a direct result of my powers then I just assume they're something like an extension of mine. It's like, you can't run the same process at the same time, they'll just cancel one another out." She'd always had her own theory about it and never thought to question it until now. It was fairly simple and had holes she didn't care about filling in. Likely there were a dozen other explanations and maybe Doctor Strange could provide some new insight.