You are comparing your start to someone else's middle
Someone goes past you on the path and it appears to cost them nothing. You are working hard. They are having a conversation. In the second or two it takes them to disappear, you have already done the arithmetic and come out badly.
Or it happens on a screen. A friend posts a distance you cannot imagine covering. Somebody at work mentions their weekend long run the way other people mention doing the shopping. You say something encouraging, and then spend the rest of the afternoon quietly recalculating what you are worth.
You are seeing the result and none of the history
What arrives in front of you is always the finished thing. The time, the distance, the photograph at the end. What does not arrive is the years of ordinary Tuesdays that made it possible, or the season they spent slower than you are now, or the stretch where they stopped completely and told nobody.
What looks effortless is nearly always old work. The runner who floated past you has a history you cannot see from the side of the path, and if you could see it, a good deal of it would look remarkably like the week you are having. They were bad at this once. They were bad at it for longer than they tend to admit.
Comparison is usually a question in disguise
It is tempting to file this under vanity and tell yourself to stop being so competitive. That rarely works, partly because it is not what is going on.
Most of the time you are trying to answer a reasonable question: am I doing all right? Nobody handed you a way to answer it. There is no mark on the wall for this, so you borrow the nearest available measure, which happens to be whoever is in front of you or whoever posted this morning.
The borrowed measure does not fit. It was built out of somebody else's years, their body, their schedule, and how much of their life is currently on fire. Held up against yours, it tells you very little beyond the fact that you are not them.
The comparison that actually carries information
There is one that works. You, a couple of months ago.
Same legs, same route, same job, same sleep. If the hill you used to walk is now a hill you run up slowly, that is real. If twenty minutes used to leave you flattened and now it does not, that is real. Those changes belong to you, and nobody else's numbers can add to them or take them away.
Most people miss this progress entirely, because it arrives without any announcement. It shows up as a slightly shorter recovery. A run you did not dread. A week where getting out of the door took less arguing than it used to. Worth noticing, because nobody else is going to notice it on your behalf.
Let it be admiration instead
You are not going to stop noticing other people, and you do not need to. What you can change is where the feeling points.
When somebody goes past you looking easy, you are watching evidence that this works. A body did that. It was not always able to. Somewhere behind that stride there is a version of them standing at the door in the dark, negotiating with themselves about whether to go out at all, which is a scene you happen to know very well.
Admiration and defeat feel almost identical from the inside. What separates them is what you do next. One sends you home to think about everything you lack. The other one gets you out again on Thursday.
You started where you started. That is the only place anybody has ever started from, including the person you were watching.
Written to encourage, not to diagnose. If something hurts or feels wrong, please speak to a doctor.