North-west Atlantic rocky intertidal shores contain few species that are affected by sharp environmental gradients. As a result, these communities have been widely used as a model experimental system. Earlier studies focussed on how average differences in ecological processes can be driven by environmental differences. More recently, there is an emphasis on how variability in recruitment and ecological interactions can shape communities. In this chapter, we explore how these two distinctly different conceptual approaches – average effects versus variability in effects – have affected the course of ecological research. Our review touches on how phylogeographic history, large-scale variability in ecological processes and small-scale indirect interactions have contributed to the generation and maintenance of community patterns. We argue that human activities, including harvesting, introducing non-native species, eutrophication and climate change, are likely to increase the variability of ecological processes. We conclude that variability of ecological processes and human activities vary on a scale much larger or longer than a typical experiment. Future studies should explicitly incorporate scales that capture the role of variability on the resilience of coastal ecosystems.