My best girlfriend, who I've known for almost 20 years and has had horses all that time and NEVER had any horses be sick or die, has lost 3 within 2 years. Two of them were aged. One of those colicked and died 2 years ago. The other colicked and died last January. Last December, her 14 year old gelding colicked and died suddenly, it was a real shock. She had 2 other mares at the same place, pastured all together and they were just fine through this all. All horses are fed exactly the same, horses always have clean and warm water in the winter (automatic waterer) which she checks DAILY, her hay is fine, nothing had changed, none of the horses had been recently worked (it was winter with the last 2). I know how she keeps her horses because she lives less than 1/4 mile from me and I periodically feed her horses if she's gone. They have shelter at all times. They are brought in for grain and checked over daily.

So yes, it's possible to have a terrible run of bad luck and not be an asshat.