Ecological communities are conformed by a complex group of interacting species. Ecologists tend to simplify their life by breaking the problem into smaller pieces and focusing, for example, on a single trophic level, or on a single type of interaction. But in nature, all interactions happen simultaneously. I present a joint effort to capture real-world complexity onto an ecological theory that allows us to understand species persistence. Overall, I show using mathematical, observational, and experimental approaches, how the network of species interactions constrains the opportunities of species to coexists. Only by including antagonistic and mutualistic interactions simultaneously, we can understand how communities persist.