He's absolutely going to make mistakes, there is no doubt about it. He's a young defenseman and he's still only been playing the position for four-ish years. If people expect him to be flawless or even close, then yeah, there will be disappoinment and things will get messy. That goes for any player with high expectations.
His package of tools is elite. I don't believe that in the 20+ years I've been around HF, I have ever declared unequivocally that one of our prospects has truly elite tools. I think Miller does, and that if they come together, he will dominate. It's hardly a guarantee, but I obviously feel very strongly about the kid.