I recently completed a migration from one server to another of a service I manage that affects over 4,000 users, and it all went off without any interruption or degradation in functionality. The few issues that did arise (one software bug in a tool I wrote that affected a team of 11 people, for which I had a workaround and fix same-day) were impossible to foresee, as my small team and I cannot test for every scenario; we can only be reactive in certain situations.
My manager considers the migration "a failure" (his words) because the team we directly support - those 11 people that were affected for a few hours by the bug, which again, was rapidly fixed and had an immediate workaround - had to use a workaround at all; in his words, "a step backwards."
I feel like he's missing the big picture, and I was pretty insulted by his characterization of this huge project that involved multiple teams and went smoothly for over 3,989 people. I made that clear in our one-on-one after the migration, but I feel like his "striving for perfection" (again, his words) leads to unrealistic expectations. How do I give constructive feedback to him about my thoughts on why the project was a success?