Opening the book…
An equipment grounding conductor protects you only if it is unbroken from the device all the way back to the service bond. Break it anywhere, a loose lug, a painted-over connection, a corroded joint, a ground wire left off during a repair, and every enclosure downstream loses its fault-clearing path. The failure stays invisible until a fault energizes a case that should have tripped the breaker and instead sits there live, waiting. Continuity is not a one-time thing set at install; connections, corrosion, and later work can quietly destroy it.
Make grounding connections tight, clean, and on bare metal; scrape paint and remove corrosion at bonding points. Use listed connectors and proper grounding screws, not sheet-metal screws or wire simply wrapped around a bolt. After work, confirm continuity from the device ground back toward the panel with a tester or low-resistance ohmmeter. In metal-conduit systems that rely on the conduit as the ground path, verify the couplings and connectors are tight, since a backed-off fitting breaks the path. Restore every ground you disturb.
Metallic raceway and cable armor may serve as the equipment grounding path where listed for it, but flexible connections and long runs often require a supplemental ground wire; know which applies. Isolated-ground circuits keep a separate insulated ground for noise reasons but still need a continuous bonding path. If you cannot confirm continuity, treat every downstream enclosure as potentially unprotected.