It is well known that many electrochemical devices such as fuel cells, electrolyzers, batteries, etc. degrade under various operating conditions. Many devices are based on solid electrolytes. In many cases, degradation manifests as electrode delamination and/or cracking of the electrolyte. An apparently obvious conclusion often reached is that this must be due to weak interfaces and some approach to mechanical strengthening or toughening should alleviate the problem. It is the intent of this manuscript to show that such electrochemical degradation often occurs due to electrochemical-mechanical coupling effects which result in extremely large internal pressures. So large can be the pressures that no amount conventional strengthening or toughening can prevent degradation. In fact, even a perfect lattice can be disrupted by electrochemically induced pressure leading to failures. In order to prevent failures, it is necessary to fully understand the role of coupling and develop strategies of mitigating high pressure formation by optimizing ion and electron transporting properties of the membrane. This manuscript discusses a fundamental mechanism of electrochemical failure of solid oxide fuel cells, solid oxide electrolyzer cells, and oxygen separators based on oxygen ion conducting solid electrolytes. Experimental results on two types solid electrolyte cells are presented in support of the mechanism.