There was a guy that did a good write up years ago about the trauma he suffered when he went to ride his motorcycle a few laps around the inside of his parking garage to dry it after he had finished washing it. That "ONE time", he did not wear a helmet. He was going about 5mph, hit a small patch of radiator fluid that had leaked from someone else's vehicle. The front washed out instantly. In the next instant, his face hit the rear bumper of a parked car. He spent a long time in the hospital... He had to have facial reconstruction surgery and had a trache tube for something like six months
I read another report from a young lady that was doing the " just down to the corner store" run on her SV650. Someone squeezed her into the curb, causing her to crash. It was the one time she did not wear her riding pants. Her knees got trashed. She was no longer able to ride even after she mostly healed. Sadly, her other favorite thing to do was gardening. Not being able to get down on her knees kind of killed that as well. I guess now, she could to raised bed gardening.
Of course, just falling down while walking, or getting out of the bathtub, can result in serious head injury. Life is risky even when you think you are playing it safe. You don't even have to leave your home... I guess ultimately, it is about playing the odds and hoping you win every time. It is so easy to think, "It's just this one time..." Odds are, you would be fine. But, there are so many of those kinds of stories like the ones above that every time I start to think, "It's just this one time...", "It's only a few miles...", "I won't be going fast...", etc... I stop and think about those stories. It is not that I NEVER go without gear, but thinking about those kinds of stories stops me from making it a habit, which I think is where the odds stop working in your favor.