Glass can support a lot of compression, but when you have a glass plate and push against it, it is the opposite side you’re pushing on that will break and then it will spread out. Glass is good with compression, not so much with expansion.
In the video from above you can see that the glass piece bends and after a while it breaks. To make the glass stronger we need to make sure that the surface is coated and has some impurities that will make the glass compress on the longitudinal axis. This way, when you push, the surface that will be extended is already compressed and will last longer.
This is the way Gorilla glass has been strengthened out. One interesting bonus fact about glass: you can burn and metl sand to become glass, but you can never burn and melt glass to obtain sand back again.