Whoever wrote your plan was not tired at the time
At some point you sat down and worked out what you were going to do. Four days a week, maybe five. Distances written next to them. A rest day put somewhere sensible. It took a while to get right and it looked good when it was finished, and for the first stretch you did roughly what it said.
Then a week arrived in which you managed about half of it. The plan stopped being a thing you were following and became a thing you were behind.
The hour the plan gets made
Think about the state you were in when you wrote it. You had time to sit down with it, which already tells you something about that afternoon. You were not exhausted, because nobody designs their training while exhausted. Exhaustion produces entirely different decisions. And the week you were planning had not happened yet, so it had nothing in it. An empty week looks enormous. There is room in it for anything you care to put there.
So the author of your plan was rested, interested, and in the first hours of having decided something, which is one of the better feelings available to anybody. They were also working from a week with no late meetings in it, no evening that collapses on Thursday, nobody else's needs arriving at seven o'clock. None of that was visible from where they were sitting.
The person who has to do it
The plan reaches you later, in worse conditions, as an instruction from someone who is no longer available for questions. It is Tuesday at nine. You have been upright since six. The plan says forty minutes and it says it in exactly the tone it had on Sunday, with no knowledge of anything that has happened since.
Which means you are not measuring yourself against a reasonable standard. You are measuring yourself against a forecast written by the most optimistic version of you there is, and you are doing it at the end of a long day. There is only one way that comparison can come out. Run it for a few weeks and the plan quietly changes job. It arrived as a guide and it has become a record of what you keep failing to do.
The plan was wrong about the week, not about you
When the two do not line up, nearly everybody draws the same conclusion. The plan was sound and they are the faulty part. The schedule was right there in black and white, after all, and they are the one who did not manage it.
But a plan is a prediction. It was a guess about how much room the next few weeks would have in them, made before any of those weeks turned up. When a prediction misses by that much, the ordinary response is to revise the prediction. You would not keep a forecast that had been wrong four weeks running and start wondering what was defective about the weather.
The unfinished weeks are telling you something specific and useful: there is less space in your week than you assumed when you were sitting down with an empty calendar. That is worth knowing. It costs you nothing to accept, and the plan can be brought down to meet it. The thing you cannot do is keep the plan where it is and try to become a person who never has a hard Tuesday.
Write one you would keep on a bad day
So build the next one from your bad evenings instead of your good ones. Think about a Tuesday when you are flat and the day overran and the weather is nothing special, and work out what you would still be willing to do on that evening. Twenty minutes, probably. Maybe a walk that turns into a few minutes of running. Set the plan there.
It will look unambitious written down, and that is the point of it. If it says twenty minutes and you do twenty minutes, the week worked. On the evenings you feel better than expected you can go longer, and nothing is stopping you. What you want is a level you can hold on the worst day of a normal week, rather than a target that only a good week can reach.
A plan that small does something the ambitious one cannot. It keeps you in contact with the habit through the weeks that go badly, and those are the weeks that decide whether any of this is still happening in six months. The heroic schedule survives until the first difficult stretch and then takes the whole project down with it, because you end up quitting the running when what actually failed was the arithmetic.
The plan is not your employer. You wrote it, on a good afternoon, with the best intentions and almost no information about what was coming. You are allowed to overrule it from inside the evening you are actually in.
Written to encourage, not to diagnose. If something hurts or feels wrong, please speak to a doctor.