The reason milestones are spaced unevenly on purpose

One loyalty scheme rewards every fifth purchase, like clockwork. Another rewards on the third, then the eighth, then the ninth, then the fifteenth — no discernible rhythm. The irregular scheme keeps people buying through the flat stretches, because a reward could be one purchase away at any point and there is never a safe moment to coast.

What everyone sees

Evenly spaced milestones look fairer and clearer — you always know where the next reward sits, which seems more motivating. Predictability is exactly what lets people ration their effort, working hard just before a known reward and coasting after it. Uneven spacing removes the map: when the next milestone could arrive at any time, every action carries a live possibility of payoff, and the coasting that regular schedules permit becomes impossible.

What is actually happening

Ferster and Skinner’s schedules of reinforcement showed that variable-interval and variable-ratio schedules — rewards arriving after unpredictable amounts of time or effort — produce steadier, more persistent responding than fixed schedules, which generate a characteristic pause after each reward. Lattal’s work on the timing of reinforcement confirms that unpredictability in when a reward arrives sustains behaviour across the gaps that a predictable schedule leaves slack. Unevenly spaced milestones are a variable schedule dressed as a reward ladder: the irregular gaps prevent the post-reward pause and keep every interval live, so effort never subsides into the lulls a regular ladder invites.

Why it stays hidden

The design hides because irregular spacing is easily read as arbitrary or even generous — an unexpected early reward feels like a bonus, not a schedule. The person does not perceive that the absence of rhythm is the mechanism, since each individual reward is welcome and each gap is endured hopefully. Because no one is shown the schedule as a whole, the pattern of unpredictability that drives their steady effort is never assembled into something they could recognise.