[bitcoin-dev] block size - pay with difficulty

[Gregory Maxwell]

On Thu, Sep 3, 2015 at 4:05 AM, Jeff Garzik via bitcoin-dev
<bitcoin-dev at lists.linuxfoundation.org> wrote:
> (b) requiring miners to have idle
> hashpower on hand to change block size are both unrealistic and potentially

I really cannot figure out how you could characterize pay with
difficty has in any way involving idle hashpower.

Can you walk me through this?