Chaos engineering is the discipline of intentionally injecting failures into a system in a controlled manner to discover weaknesses before they manifest as unplanned outages. Rather than waiting for production failures to reveal system limitations, chaos engineering proactively tests whether a system behaves as expected under adverse conditions. Netflix pioneered the practice with Chaos Monkey in 2011; it has since become a standard SRE practice at organisations of all sizes.
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.