This article is the first in a two-part series discussing declining standards of care. Many healthcare organisations, particularly hospitals, are under increased pressure to maintain standards of care while experiencing funding and staff shortages, and increasing patient numbers and demand for services. One of the main risks associated with these competing demands is a gradual decline in care standards, described as ‘care erosion’ in this article. Understanding the psychosocial mechanisms that can lead to care erosion is important in preventing its occurrence. This article uses the theory of cognitive dissonance to explain how nurses reflect on, and maintain, quality of care. If practice is suboptimal or substandard and inconsistent with nursing values, standards or regulations, nurses are likely to experience inner conflict or ‘dissonance discomfort’ and will usually attempt to reduce this feeling by enhancing the quality of care they provide. Conversely, nurses may defend, deny, trivialise or ignore substandard care. The authors suggest that this is the mechanism that leads to care erosion. This article uses three scenarios to explore the nurse’s role in care erosion. Part two of this article discusses the wider involvement of individuals, organisations and nurse education in preventing care erosion.