Physical Danger
Working around large pieces of equipment, chemicals, pressurized systems, and extreme temperatures can be dangerous. That's why you never hear, "Training-shmaining. What's the big deal?"
You need to understand phrases like "Don't stand there," "Look out," and "That pressure gauge cannot read your headache so take the valves out of your ears."
The best idea is just to follow all safety guidelines, even the ones that seem overly cautious. They're probably there because at some point somebody somewhere was hurt ignoring a rule. Even if you've never heard of anyone falling while running with scissors in their hand, you don't want to be the reason someone else says, "Told you so."