During an internship in California in college I was lucky enough to bring my bike with me to enjoy but had to wear a helmet as its state law. I hated the idea of wearing one since I rarely did back home but am fortunate as I got into a seemingly minor wreck. Pulling off a canyon rode I unexpectedly hit a gravel patch and got pinned under my bike until a bystander helped me up. I was scrapped up a bit but fine. It wasn't until I got home later that evening I noticed a nice sized puncture in the helmet from my head hitting a rock. Without the helmet I would have likely been knocked unconscious or worse.
I used to care about how I looked on the bike, not wearing a helmet, but have come to the obvious reasoning that safety is more important. Do I miss the feeling of the wind in my face as I ride? Sure, but getting home safe matters more. If I ever get a bike again I won't leave home without one.