Most of the runs you skip are ones you had time for
You get in at seven. Something is happening at eight. You do the arithmetic in the hallway, still holding your keys: forty minutes, minus getting changed, minus the shower afterwards. That leaves maybe twenty-five minutes of actual running. Not really worth it. So you put it off until Saturday, when there will be proper time.
Saturday turns out to have its own plans. And the week closes with one genuine opportunity that arrived too small to be accepted, and one imaginary opportunity that never arrived at all.
Where your minimum came from
Ask yourself what counts as a real run and a number comes back almost immediately. Five kilometres. Half an hour. Forty-five minutes if you are taking it seriously. Now ask where that number came from, and most people cannot say.
It was inherited. Race distances are round because a race has to be organised and advertised, not because anything happens to a human being at five kilometres that does not happen at three. The training plans you read were written for a general reader with an unspecified life. Someone at work mentioned that they do ten and it lodged somewhere. None of it was chosen with your Tuesday evening in mind, and you have been using it to veto your Tuesday evenings ever since.
What the rule quietly costs you
A minimum of an hour means you can only run on days shaped a particular way. Nothing running late, nobody needing you at home, weather you can live with, and enough left in you when it is all done. Days like that are rarer than they appear at the start of a week.
So the runs become scarce, and scarcity does something unhelpful to them. A run you only get one of has to go well. You set out with something to prove, go harder than the day deserves, and come home having had a worse time than you would have had on a short easy one. Then you are less keen to repeat it, which is not the reaction anybody is aiming for.
Meanwhile the person going out for twenty minutes a few times a week is doing more running than you are and thinking about it a great deal less.
Nothing switches on at minute thirty
There is no line in your body where the effort starts to count. The first fifteen minutes of a long run and a fifteen-minute run are the same fifteen minutes. Your legs have no access to what you originally intended.
And most of the difficulty in running is not in the running. It is in finding the shoes, opening the door, getting down the first street, and surviving the small negotiation you hold with yourself while you are still deciding whether this is happening. A short run makes you do every one of those. That is most of the work of being someone who runs, and it is done in full whether you are out for fifteen minutes or ninety. Whatever fitness you are building comes from how often this happens rather than from any single session being long enough to respect.
Take the window in the shape it comes in
Decide the answer before you are standing in the hallway with your coat still on. If there are forty minutes, the run is twenty minutes out and twenty minutes back, or as near to that as the roads allow. You are not shortening anything. That is simply the run that Thursday had available.
Then watch what you call it afterwards. The word to notice is only. It shows up the moment you start measuring a run against one you did not do, and it turns a perfectly good half hour into a small failure you now have to carry around. You went out. On a day you very nearly did not.
Try it for a fortnight and the count changes more than you expect, because the short windows are the ones that keep turning up. The long clear morning is not coming to rescue the week. The forty minutes on a Thursday is what is genuinely on offer, and it is enough to be going on with.
Written to encourage, not to diagnose. If something hurts or feels wrong, please speak to a doctor.