You can't let him "go into a cave" and then come out with something lacking after a bunch of time has passed. Given what you know about him, it's your job to h

You can't let him "go into a cave" and then come out with something lacking after a bunch of time has passed. Given what you know about him, it's your job to hold him accountable, keep an eye on him, and make sure that _all_ aspects of the project are being accounted for. It's not going necessarily going to be fun or comfortable for anyone, but you should err on the side of micromanagement until he is performing at a high level. You probably also need to be very clear about the totality of what is expected - yes, a cool design is great, but it must have tests, it must be communicated to others (be that by documentation, a presentation, training, etc)... and no amount of "design" or "don't have time" excuses will substitute for these aspects.