If something fell on you, and you got hurt, it might be hard to prove someone else’s negligence caused that problem. For example, maybe someone stocked a shelf and then left an item really close to the edge, too close. Then, when someone lightly bumped the shelf, it fell on you. But how do you know they stocked the shelf wrong? Now this may or not be an instance where this applies, but, sometimes, the thing speaks for itself. And this is called the legal doctrine of “res ipsa loquitur”.