Progressive overload

Progressive overload is the principle that, to keep improving, you must gradually increase the stress placed on the body — most commonly by adding weight or reps, but also through more sets, better range of motion, or reduced rest.

It matters because the body adapts to a given stimulus and then stops changing; without a progressive increase, progress stalls. It is the single most important principle behind getting stronger or bigger.

In practice, it is applied by tracking your lifts and beating a previous session — an extra rep, a little more load — in a structured way rather than adding weight randomly.