Yes relapse is definitely not an unintentional or passive event. It may be triggered by unconscious impulses, but ultimately it's always the result of conscious action. In my view, probably the expression "falling off the wagon" or "relapses happen, just dust yourself off and jump back on" arose to kinda augment the shame, guilt, and other emotional consequences of relapsing. They may provide some relief in the moment, but only temporarily, just like what the expression suggests. We humans often look for sneaky ways out and ways to justify them
