KISS principle states that systems are more reliable and understandable when they are kept simple rather than made complicated. KISS stands for "Keep It Simple, Stupid". While this principle was originally intended for aircraft design, it is also very applicable to technical systems and reliability engineering.
Complexity is the enemy of reliability.
More complex systems tend to have more points of failure and more unpredictable interactions between components. Look at Kubernetes 🥲. It requires team(s) of engineers to maintain as it's highly dynamic and complex. Simple designs are easier to understand, troubleshoot, and maintain.
Some ways the KISS principle promotes reliability: