User blog comment:12th Supernova/Chapter 786: 10 Minutes/@comment-5398287-20150514092704

What interests me is that there's a way to turn Haki off, or at least cut off one's access to it, even if that's part of a drawback to a certain technique. Didn't think it was possible to set a limit for one's spirit. I'm guessing this is why Law was concerned about Luffy overexerting his Haki last chapter, which means it's not exactly an endless wellspring of power to use.