I like OP's post but would love to get some empirical data.

> If I’m “hyper-productive” and “focused” on my “worst day”, it obviously wasn’t my worst day?

Good q, I could also have asked: What's your system to overcome set-backs which usually distract you and turn an ok day into a bad day. Or just, how to turn a lazy or bad started day into a good day.

(1) Separate work from life, be able to walk away for a bit when work isn't going well. And do walk away if things aren't going well. If you haven't been able to write any code for the past few hours, odds are you won't be able to write any in the next few hours.

(2) Focus on process over results. IE have a good process to minimize the amount of time you spend thinking about what you should be doing, whether you did the right thing, etc. What honestly helps in these cases is just having a task list of "I need to get XYZ done today" and then blasting through it without leaving room for thinking about things too much. I like Getting Things Done (ie https://www.amazon.com/Getting-Things-Done-Stress-Free-Produ...) because it helps separate work from life.

(3) Take the long view of your life/career. The truth is that you are going to make mistakes, bugs will get into prod, you're going to get burned out, etc, so you need to accept that you will have "bad" days (or days, weeks, moths where you just don't care about what you're doing in which case it is obviously going to be crap) and focus on the process for improving them to minimize them over the long run. I think the important question here isn't "did I make mistakes" but rather "is my process resulting in a slower rate of mistakes/less severe mistakes.

(4) Never forget to eat, sleep, drink water, and exercise. Especially sleep. when things are bad we tend to sacrifice sleep, that almost always makes it worse.

Most of it I think is summarized as having a process you can trust so that when things do go poorly you can focus on the process in those moments. The process will get you out.