Petrarch’s Principle, named here, is to know things unseen, yet to ignore things seen. We apply the principle to the debate over the appropriate role and utility of human-made reefs (HMRs) in fishery and ecosystem management by reviewing four linked issues that were discussed at the recent 7th International Conference on Artificial Reefs and Related Aquatic Habitats. First, deploying protected HMRs can help to mitigate the depletion of fishery stocks through overharvest and habitat degradation. Secondly, to achieve this objective effectively, it is essential that HMRs are protected as no-take areas, and that, thirdly, HMRs are large, well-planned, evaluated and monitored. Finally, ecosystem modelling and adaptive management responses are necessary to forecast and manage the benefits of HMRs. Moreover, uncertainty about the resolution of the well-rehearsed attraction/production debate may be resolved by ensuring that HMRs are managed as protected no-take areas. And to ensure an unbiased attitude that will aid the clarification of consequences, costs and benefits, we propose a change in terminology, from artificial reefs to human-made reefs.