By meeting in the hallways with colleagues, we have come up with serendipitous ideas. These ideas are usually within our domain of expertise. These I think of as “micro-serendipity” (microS). On the other hand, by meeting for lunches — or even retreats — with people from other disciplines, we have come up with more significant, broader, potentially-higher-impact ideas. These I think of as “macro-serendipity” (macroS). MicroS advances the ideas in a given field, in ways that are usually somewhat predictable and frequently important. MacroS can create a new field. Both microS and macroS are important, at the right time. Are you doing one, and need to try the other more often?