Societies need to build resiliency into these systems in order to achieve such a feat. Resilient systems work to “ensure that functionality is retained and can be re-instated through system linkages”[31] despite some failures or operational disturbances. Ensuring the functionality of these important systems is achieved through instilling and maintaining flexibility in the presence of a “safe failure.”[31] Resilient systems achieve flexibility by making sure that key functions are distributed in a way that they would not all be affected by a given event at one time, what is often referred to as spatial diversity, and has multiple methods for meeting a given need, what is often referred to as functional diversity.[31] The presence of safe failures also plays a critical role in maintaining these systems, which work by absorbing sudden shocks that may even exceed design thresholds.[31] Environmental disturbances are certainly expected to challenge the dexterity of these systems, so the presence of safe failures almost certainly appears to be a necessity.