Last week at Northstar:
A dad skier was bending down to zip up his toddler daughter's jacket in the base area near a fence. A pair of skis were leaning up against the fence two feet away from dad. Some doofus backed up into the skis, causing them to slide and fall down the fence crashing directly into dad's head. Luckily, he had his helmet on. If he didn't, he'd most certainly have had to go to the hospital for something.
You wear a helmet because doofuses have a knack for being unforeseeable.