One of my mates tried to encourage me to stop running once as he said it would be bad for my knees. This belief was that I should stop running in case I got an injury which meant I couldn't run (but could walk ok). That made no sense to me - why stop doing someone to avoid the risk of having to stop it later.
As an asthmatic, I suppose my risk factor is bigger than most peoples as I could have an attack at any time. Given I don't generally keep my inhaler on me when I run, this could be quite dangerous so I've started making sure I always have it on me when I'm in remote locations. Saying that though, running actually makes my asthma better, so the risk I'm taking is a small chance of a worst situation in order to gain an improvement.
The biggest risk I've identified though is when I used to run along some woods a few years back. These are woods in the middle of a farmer's field and I never saw anyone else ever use them. It got me wondering what would actually hapen if I was to fall over a branch, break my leg and be unable to get up. No-one would be about to help me, I would be unable to move and stuck there. If it was a particularly cold night, wearing on the ground outdoors in shorts and a t-shirt might not be a good idea. Given I live on my own, it could be a few days before anyone noticed I was missing, and no-one would know where to look for me.
The biggest hazard I've ever faced though as a few years ago being very stiff after a half-marathon, relaxing in the bath and my leg muscles really tightened up. They were so tight I was unable to get out of the bath. Living on my own, all sorts of stuff started going through my mind about what happens if I can't get out for days and end up trapped in the bath for ages after the water got cold. As my bathroom is tiled and enclosed (no outside walls), shouting for help wouldn't be much use. Needless to say after another while in the bath my muscles relaxed so there was no problem at all.
Anyway, as you can tell, I like to put cheery ideas into people's heads at the start of the weekend.