I don't understand how people can be so irresponsible with their stuff. I have a pair of Oakleys I bought 6 years ago that are in almost perfect condition. I've sat on my sunglasses once or twice before, but I always feel them before my entire weight has been applied and stop myself from possibly crushing them. I don't drop them (when they're not on my face I put them on my head, clip them onto my shirt's collar, or clip them onto my pocket), I don't kick them (they're never on the floor), I don't use them as protection against harsher elements (when using a grinder I use a different pair of glasses, safety glasses), etc.
I don't wear the 6 year old glasses anymore (let's be honest, who still wears anything they got 6+ years ago unless it has sentimental value like a wedding ring or heirloom), but the glasses I do wear now cost like $500 and I'd be enraged if I broke them. That's enough for me to be careful with them.