Why You Use a UV Filter on Your Lenses

So this week I was photographing an extended family of seven. We were walking down a very steep path from The Peak in Hong Kong. It had been raining and the pavement was super slippery. No sooner had I told everyone to "be careful", and I stepped on some slimy moss. It all happened in slow motion, but I clearly remember looking up in the air at my feet.
The next sensation was the sickening sound of a Canon 5DMK3 making full contact with cement. My Sigma ART 35/1.4 looked like this. I reckoned it was dead.
I did the rest of the shoot with my 85/1.2. When I got home I couldn't get the filter off as it was basically fused with the lens. Upon closer inspection I saw that the lens elements might be OK.
I used my Swiss Army knife to tap out all the busted filter glass, and low and behold, the lens was fine.
So, you know the moral of the story.

Always use a UV filter on nice lenses