In settled times, when structure and its existing culture (i.e. its existing narrative account of itself) allow for relatively easy social reproduction, new ideologies are unlikely to take hold and motivate novel courses of behaviour for individuals
In unsettled times, however, people find that they can no longer rely on existing culture to explain their experience (or, in other words, their immediate experience begins to negate the existing cultural story)
In such times, culture (rather than structure) becomes the thing that motivates action and thereby moves history