I've never read the book, but I'm curious: did he do both at once, or independently then decide that both in combination gave the best result? If he stayed of

I've never read the book, but I'm curious: did he do both at once, or independently then decide that both in combination gave the best result? If he stayed off his phone and took cold showers, without testing them separately, how do we know it wasn't the cold showers that gave the result, or the lack of phone?