How Do Goggles Get Scratched?

Thanks to all responders for your input. After reviewing these responses, and some careful thought and diligent observation, I think most of my goggle scratching troubles were the result of tossing them loose in my bag. I use an Aqua Sphere swim mask now which comes with a case which I keep it in. If I'm not mistaken, however, the more common racing type goggles from Speedo don't come with a case; which seems like an important omission. For me, the critical failure mode seems to the inexorable buildup of a translucent film of scale/scum that can't be washed off. Along with my goggles, I purchased a bottle of Aqua Sphere Anti-Fog (ASAF) liquid. While I't's unclear to me that it has any particular anti-fogging capabilities, it has clearly shown itself to be excellent at cleaning the goggles. After going a long time without using the product, my goggles were getting hard to see through. I applied the ASAF all over the goggles, not just on the lenses, and it cleaned them up very nicely. That also helped them at least a little bit to not fog up; but I think the non-fogging may have had more to do with them just being clean than any special properties the Anti-Fog solution provided.

Thanks to all responders for your input. After reviewing these responses, and some careful thought and diligent observation, I think most of my goggle scratching troubles were the result of tossing them loose in my bag. I use an Aqua Sphere swim mask now which comes with a case which I keep it in. If I'm not mistaken, however, the more common racing type goggles from Speedo don't come with a case; which seems like an important omission. For me, the critical failure mode seems to the inexorable buildup of a translucent film of scale/scum that can't be washed off. Along with my goggles, I purchased a bottle of Aqua Sphere Anti-Fog (ASAF) liquid. While I't's unclear to me that it has any particular anti-fogging capabilities, it has clearly shown itself to be excellent at cleaning the goggles. After going a long time without using the product, my goggles were getting hard to see through. I applied the ASAF all over the goggles, not just on the lenses, and it cleaned them up very nicely. That also helped them at least a little bit to not fog up; but I think the non-fogging may have had more to do with them just being clean than any special properties the Anti-Fog solution provided.