A good run turns into a number you have to beat
Every so often a run simply works. You go out expecting the usual negotiation and it never arrives. The legs turn over, the breathing settles early, and you finish the loop quicker than you ever have while feeling like you could have kept going. You come home pleased with yourself, and you should. Those evenings are rare and they are worth something.
Then there is the next run, and that is where the trouble starts.
What happens the next time out
You set off on the same route with the good one still in mind. Not as a memory exactly, more as a setting. Within a few minutes you can tell this is not that evening. The legs are ordinary, the breathing is doing its usual thing, and the pace you held last week without noticing now costs you something to hold at all.
So you push, because last week says you can. By halfway you are working much harder than you meant to, and by the end you have had a miserable run on a day when a perfectly good one was available.
Then comes the story you tell about it. You were faster nine days ago. So either you have lost fitness in nine days, which is not how bodies work, or last week was a fluke and you have been flattering yourself. Both of those are wrong and both are sitting right there, which is why one of them usually gets picked.
Where the good day came from
Very little of it was fitness. Fitness does not turn up on a Tuesday and leave again by Friday. It accumulates slowly and it does not swing about by the week. What swings about is everything sitting on top of it. How you slept, and how you slept the night before that. What you had eaten and when. Whether the wind was behind you on the long straight. Whether you had spent the day being talked at. Whether your body had finished with the work you gave it on Sunday.
You controlled almost none of that, and you cannot arrange for it to line up again by wanting it more. This is the awkward part, because the good run felt earned. It felt like something you did. Mostly it was a set of conditions arriving on the one day you happened to go out.
Your best and your usual are different measurements
A best tells you what is possible when everything cooperates. Your usual tells you what your week actually looks like. The first is a ceiling you touch a handful of times a year. The second is the thing genuinely making you fitter, because it is the one that repeats.
When the ceiling gets treated as the floor, ordinary running becomes failed running. Every session is now marked against an evening that needed conditions you cannot order in advance, and you will lose that comparison most weeks. Which means the bulk of your running starts coming home with a small verdict attached to it. People do not carry on doing things that are arranged to disappoint them, and this is one of the quieter reasons a habit that was going well in month three is finished by month five.
What to do with the good one instead
Enjoy it on the day, and then let the day close. Tell somebody about it if you want to. Next time out, run the run in front of you rather than the one you are remembering.
A rough way to keep yourself honest is to judge a run by the effort it took rather than by what it produced. The effort is the part you actually brought. The rest was the weather, your sleep, and last week's training showing up or not showing up. An evening that felt steady and repeatable was a good evening, whatever number ended up attached to it.
None of this means the good ones are gone. What happened that evening was your body doing what it does when the conditions suit it, and the conditions come round again. You just do not get to pick the date. It tends to land on an evening you nearly talked yourself out of, which is annoying, and is also the reason to keep going out on the ordinary ones.
Written to encourage, not to diagnose. If something hurts or feels wrong, please speak to a doctor.