Given a choice between a demanding programme performed erratically and a modest one performed reliably, the modest one generally produces more over a year. The reason is that adaptation decays, and decay is faster than most people assume.
Adaptations reverse when the demand stops
The same logic that builds capacity dismantles it, since maintaining tissue and metabolic machinery costs energy and the body sheds what it is not using.
Measures of endurance capacity begin declining within a couple of weeks of stopping, and strength follows somewhat more slowly.
An ambitious block followed by a break therefore spends part of each new block rebuilding what the previous break removed rather than adding to it.
Maintenance is cheaper than building
Retaining an adaptation requires considerably less work than producing it, and a reduced but regular schedule holds most of the gain.
Which means the sensible response to a busy period is a smaller programme rather than a suspended one, since the small version protects the base.
People tend to do the opposite, treating a programme as something to be done properly or not at all, which converts every busy month into a reset.
Ambition raises the cost of a single session
A demanding session requires time, energy and often travel, so it is vulnerable to any disruption in a day.
Once several sessions have been missed, the programme is behind, and the gap between where the plan says a person should be and where they are becomes a reason to abandon it.
A programme with a low per-session cost survives disruption because there is always a version of it that fits the day that actually happened.
Habits form through repetition, not effort
Behaviour becomes automatic through frequent repetition in a stable context, and the intensity of each repetition contributes little to that process.
Frequent short sessions therefore establish the behaviour faster than infrequent long ones, even where total weekly work is identical.
Once the behaviour is automatic, increasing it is a small adjustment, whereas starting again from nothing requires the whole formation process to run again.
What this does not mean
Consistency without progression produces a stable capacity rather than a rising one, since an unchanging demand stops generating a signal for adaptation.
The argument is about which constraint binds first, and for most people it is attendance rather than programme design.
Which is why coaches examining a stalled programme ask how many sessions were completed before they ask what those sessions contained.