What Vander Wal realized is that socially exposed tagging for personal use introduces another organizing agent that compensates for the ambiguity of its vocabulary with high-value serendipity: people. We are much better at picking up information and knowledge cues based on perceived similarities and differences compared to other people, than we are at picking up clues from a people-free environment. If people-free environments gives us weak serendipity, person-mediated serendipity is much richer.
People are a useful organizing agent because they are natural knowledge attractors and aggregators of meaning. People habitually collect and arrange for themselves what Vander Wal calls “personal infoclouds” and these arrangements reflect a meaningful perspective on knowledge (Vander Wal 2006).