Most medical devices have been designed for safety and effectiveness, but sometimes Adverse Events (AEs) still occur. Typically, these occurrences are multifactorial, namely due to human error, technological imperfections (design, usability, reliability) and supporting infrastructure limitations (maintenance, utility supplies, and procurement processes). Understanding the complex causes of AEs requires a systems approach. AEs investigated retrospectively are not just looking for mistakes, but for lessons learned to prevent AEs from recurring. Learning requires a comprehensive understanding of the causes of the AEs.