It is a dangerous activity we all partake in, and preparedness does play a big part.
Unfortunately what often happens is you push yourself (or are already exhausted) to beat the storm/cross the river/find the trail/whatever and render yourself incapable of making good decisions. When you have no energy you lose a lot of cognitive functions, and even lose what we refer to as good instincts.

It is easy to armchair hike, and say what we would have done differently. And I think it's not a bad idea, as the more we talk about it, the more people will realize they need to be prepared for the unexpected.

There's a small mountain I hike once or twice a week after work, it's about a 1 hour round trip with a fair amount of exposure. A lot of people do it with nothing more than shorts and a tshirt, and are perfectly fine. I never attempt it without a small pack containing first aid kit, water, snack, cel phone, and windshirt or jacket depending on the season. It doesn't slow me down, but would enable me to wait out a storm or other such problem. The hardest part is knowing when to admit that summiting isn't safe, but I make it a point to check the weather reports, use common sense, and hit the gym if it looks unsafe to hike.