If a retaining wall is immobile, it incurs lateral soil pressure from both sides, and that is the so called resting pressure.
When the retaining wall, due to load from the retained soil massive, which tends to slide down (wedge of failure), starts moving towards the soil in front of the wall (and thus off the retained soil), then the resting pressure from the retained soil becomes active pressure; while the pressure from the soil in front of the wall, resisting against the wall moving towards it, becomes passive pressure (displacement wedge pressure).
Active pressure is less than resting pressure, while passive pressure always exceeds resting pressure. Practically, some centimeters movement is sufficient to completely realize passive pressure; as well as practically not any retaining wall undergone active pressure remains completely immobile.
As far as the wall so moves, the shifting force (due to active pressure) is reducing, while resisting force (due to passive pressure) is increasing.
As soon as growing passive pressure load becomes equal to active pressure load, the wall stops moving. As a rule, if the retaining wall is designed adequately, the passive pressure does not reach its maximally possible value.
To summarize: active pressure acts actively, it holds, let's say, 'first-mover right' trying to 'push off' the retaining wall. While the passive pressure will not 'respond', until it is 'attacked' by wall pushed by active pressure.