Biosphere 2 failed because of a lack of knowledge of how nature really worked.

Biosphere 2 was an experiment in which eight individuals were sealed inside a closed, self-sustaining ecosystem for two years. The project failed to achieve its intended goals due to several factors, one of which was a lack of understanding of how ecosystems function in the real world. The design of Biosphere 2 didn't take into account the complex interactions among the various organisms and ecological processes, leading to significant ecological imbalances and crop failures.