Fault injection is the technical implementation of chaos engineering — the specific tools and techniques used to introduce failures into a running system. Game Days are the organisational practice of running fault injection experiments in a scheduled, team-wide session with defined scenarios, observers, and debrief. Together, they form the operational backbone of reliability testing: fault injection provides the tools, Game Days provide the discipline and coordination.
Analogy🏏Cricket
🏏 Think of it like cricket: A batting coach who only reviews a batter's technique after a tournament has already ended. The batter has played 10 matches with a flawed grip — every run scored with bad technique is harder to unlearn than if the coach had corrected it in the first net session. Shifting security left is bringing the coach into the net sessions, not the post-tournament review.