A few years back a friend and I ran the same swing progression for a couple of months. Same weights, same days, same everything, mostly because it made it easier to compare notes. By week eight he had moved up a bell. I was still on the one I started with and my sets felt worse than they had in week two.
The easy read is that he worked harder, or I was undertrained, or one of us had picked the wrong weight. I don't think any of that was true. And I suspect most people who have trained next to someone for any length of time already know it isn't, even if the conclusion never quite survives contact with the next program they download.
The part nobody argues with and nobody acts on
Put a large group of people on an identical program, supervise every session so you know the work actually got done, and measure them at the end. The results do not cluster. Some people add a great deal of strength. Some add a little. A real minority barely move at all despite completing every prescribed session.
I'm not going to hand you a percentage. The figures move around depending on the study, the population and what was being measured, and quoting one precisely enough to sound authoritative is how you end up being wrong in public. You don't need the number anyway. You have watched this happen in your own gym.
What is worth sitting with is that the spread exists after you control for the work. Everyone did the program. The program was not the variable.
Nothing about this is a straight line
Two things go wrong when people picture their own progress.
The first is expecting it to be linear. Strength does not accumulate at a steady rate, and neither does size. Early on almost anything works, and a lot of what looks like new muscle is your nervous system getting less cautious. Later the same effort buys a fraction as much. Most training plans are written as though the rate were constant, because a constant rate is the only thing you can put in a spreadsheet.
The second is treating recovery as a fixed cost. It isn't. It moves with sleep, with how much life is currently asking of you, with age, with how long you have trained, with what you have eaten, and with a genetic component nobody gets to pick. A Tuesday session that costs you very little in March can cost you a great deal in November, with no change in the numbers on the page.
So the honest picture of your own progress is a line that climbs, flattens for longer than you would like, dips somewhere you didn't plan for, and climbs again. Anybody selling you a smoother version of that is selling you the spreadsheet, not the outcome.
What a fixed plan actually is
Here is the part that took me longest to accept.
The problem with a written program is not that it is wrong. A good program is a good guess, and a good guess beats no plan whatsoever, which is what most people are actually running. The problem is that it has no way of finding out whether the guess held. Week six prescribes what week six prescribed on the day it was written. Nothing that happened to you in weeks one through five reaches it. It cannot know that you slept badly for nine days, or that the weight it chose was already too light by week three, or that your last session was the best one you have had all year.
Copying the session out of somebody's video is the same problem with the serial numbers filed off. That is a guess about a stranger, made by a stranger, and you are the third party to it.
None of this is an argument against structure. I sell programs. Wandering into the gym and doing whatever appeals is worse than following a plan written for somebody else, and it is worse by a wide margin. The argument is against structure that cannot hear you.
The loop, which is unglamorous
The fix is not a cleverer template. It is a feedback loop, and it has three parts that are all boring.
Measure something objective. Reps completed against reps prescribed, the weight, whether the last set moved like the first one. It does not have to be exotic. It has to be the same measurement every time, or you are comparing noise.
Record something subjective. How hard it was. Whether you would have taken another set. Effort ratings get sneered at by people who want everything instrumented, and they are the single most information-dense thing you can collect in five seconds. The catch is that they are only useful if you are honest on the days you don't want to be.
Let the next session move. This is the step everybody skips. Data you collect and never act on is a diary. If a run of hard-feeling sessions doesn't eventually change what you are asked to do, you have built a very tidy record of getting nowhere.
Do that for a couple of months and you have something a program cannot give you: a picture of how you respond, which is the only response rate that matters to you.
Where we come into it
This is the whole reason BellSense exists, so I'll be brief and stick to what it does rather than what I would like you to feel about it.
You log the session and rate the effort. If you wear a strap, it reads what your heart rate did inside the workout. If Apple Health has your sleep and resting heart rate, it reads those too. Then every tracked block gets one of three verdicts: advance, hold, or back off. Open the next session and the prescription has already moved.
The part I care about most is what it compares you to. Your movement baselines are yours, built per exercise and per weight, and they only start overriding the defaults once there are enough reps at that weight to mean anything. Readiness is scored against your own trailing averages, not a population chart. Heart rate drift is measured against earlier in the same session. Even the ceiling used for cardio zones prefers a peak you have actually hit over the formula everyone else applies to your age.
Every number BellSense compares you against is one of yours.
It will not make you a responder if you aren't one, and it cannot tell you your rate in advance. Nothing can. What it can do is stop pretending week six knows something it doesn't.