Exemplar search results in gradually less representative items
If one is tasked with coming up with many exemplars of a concept, then they will typically start with the most representative ones, and then slowly exhaust their way around the conceptual periphery of that concept. This progressive increase in difficulty in coming up with exemplars can make challenging tasks more accessible (e.g. coming up with many alternative representations in fine arts, reaching back to many old friends). This also resembles a process of hierarchical clustering.