You buy a new lawnmower. The engine starts, the blades spin, and you push it across the yard. You assume the manufacturer did its job: built a machine that works and told you how to use it safely. But what if the mower kicks a rock through your neighbor’s window, or worse, sends a piece of metal into your leg? What if the instruction manual never mentioned the danger of thrown objects? That missing warning can turn a purchase into a lawsuit.

Product liability law holds manufacturers responsible when their products cause harm. One of the most common routes to that liability is a failure to warn. In plain terms: if a product has a risk that a normal person wouldn’t know about, the manufacturer must tell you. If they don’t, and you get hurt, they may have to pay.

The law does not require that every product be perfectly safe. You cannot buy a knife and sue because it cuts you. But the law does require that manufacturers warn about hidden dangers—risks that are not obvious from looking at or using the product. A lawnmower blade obviously cuts grass. Not so obvious: a mower can pick up a small rock and hurl it at high speed. That is a hidden risk. A manufacturer who fails to put a warning on the mower or in the manual about thrown objects is leaving the door open for a product liability claim.

To win a failure-to-warn case, a plaintiff must show that the manufacturer knew or should have known about the danger. This is not a hard standard. Manufacturers test products. They have engineers and safety experts. They run simulations. If a risk exists and the manufacturer could have discovered it through reasonable testing, the court will assume they knew about it. Then the question becomes: was the warning adequate?

Adequacy is key. Sticking a tiny line of text on page 14 of a manual is not enough. Courts look at the warning’s size, color, placement, and language. A warning must be conspicuous—something that catches your attention before you start using the product. It must be specific, not vague. “Use caution” is worthless. “This mower can throw objects up to 50 feet at speeds exceeding 100 mph. Keep children and pets at least 75 feet away” is specific. It tells you the risk and gives you a concrete action to avoid it.

When a warning is missing or badly written, the manufacturer cannot blame the user for getting hurt. The legal term is that the warning must be “adequate to make the product reasonably safe.” If the warning is not adequate, the product itself is considered defective. That defect exists regardless of how well the mower cuts grass. The product is legally unsafe because the user was not properly informed.

Take a real example. In the 1990s, a major power tool company sold a circular saw without a warning about kickback—a sudden, violent reaction when the blade binds and the saw jumps backward toward the user. Thousands of injuries occurred. Courts found the company liable because they knew about kickback but only buried a vague caution in the manual. The company had to pay millions in damages and redesign their warnings.

What counts as a bad warning? Anything that downplays the risk, hides it behind technical jargon, or puts it in a place nobody will read. A warning printed in gray ink on a silver label is a bad warning. A warning that says “risk of injury” without saying what kind of injury or how to prevent it is a bad warning. A warning on a child’s toy that says “not for children under 3” is a bad warning if the real danger is small parts that can choke a six-year-old. The law expects manufacturers to think like the people who will actually use the product—not like lawyers writing disclaimers.

The consequences for a manufacturer can be severe. A court can award a plaintiff medical costs, lost wages, pain and suffering, and sometimes punitive damages if the manufacturer acted with reckless disregard for safety. For a small company, one lawsuit can mean bankruptcy. For a large company, a pattern of bad warnings can lead to class-action suits and government recalls.

But the real point is this: the warning on a product is not just a piece of paper. It is a legal promise that the manufacturer has told you what you need to know to stay safe. When that promise is broken—by omission, by small print, by vague language—the law steps in. If you have been hurt by a product that never warned you about the danger that caused your injury, you may have a product liability case. And the manufacturer may be paying for more than just a new lawnmower.