Let me give a few. A motorcycle accident broke an arm, and the other person left with no insurance information (my brother's arm is recovered). A propane accident lead to burns over 30% of his body (my brother-in-law Abe survived with significant scarring, but it was touch and go for a while). Hodgkin's lymphoma (killed Mark). A stumble leaving a Halloween part lead to falling with the corner of the step hitting her backbone (Ardith is partially paralyzed + has other health problems). Cancer of the small intestine lead to major surgery and months of chemo (Euna looks like she will survive). A brain cyst lead to balance problems and could have been lethal had it not been for expensive brain surgery (I know 2 women this happened to, both are nicely recovered but one had to never have kids). A jump on a dirt bike went wrong when there proved to be a mine shaft on the other side of the hill he jumped over (Matt is now paraplegic). Oh, and then we have depression leading to suicide attempts (I knew multiple people who succeeded).

Then there is the chronic stuff. I know multiple people with diabetes, several more with Chrohn's disease. Severe allergies are common and can be expensive. Schizophrenia hits 1% of the population.

These are just some of the people I personally know that stuff happened to. Most (luckily) were covered by someone's insurance. But not all.

Yes, you can roll the dice and play roulette. Yes, young people feel immortal. But stuff goes wrong often enough that you're highly advised not to if you have a choice. If you pay attention and live a while, you too will collect a nasty list of sad examples.