A recent and prominent claim for the value of biodiversity is its importance for sustaining multiple ecosystem functions. The general idea is intuitively appealing: since all species are to some extent unique, each will be important for a different set of functions. Therefore, as more functions are considered, a greater diversity of species is necessary to sustain all functions simultaneously. However, we show here that the relationship between biodiversity and ecosystem functioning does not change with the number of functions considered. Biodiversity affects the level of multifunctionality via non-additive effects on individual functions, and the effect on multifunctionality equals the average effect on single functions. These insights run counter to messages in the literature. In the light of our simulations, we present limitations and pitfalls with current methods used to study biodiversity-multifunctionality, which together provide a perspective for future studies.