Bests & Worsts Reviews from Amazon

There was once a time when I would have given this product a glowing 5 star review. I loved this these hooks when I first discovered them; the walls in my home are practically made from concrete which makes putting nails in extremely difficult bordering on nearly impossible. I had several pieces hanging on my walls using different sized strips/hooks, all of which were hung around 5 to 6 years ago (maybe longer) over a period of approximately a year+. The product worked exactly as intended until suddenly a few months ago I hear a loud noise in another room and discover a framed piece had fallen from the wall. After all this time the adhesive backing completely failed completely, the back of the hook was no longer sticky at all. I assumed it was a freak accident and a few weeks to a month later the same exact thing happened (luckily this piece was hung using two hooks and only one failed). Still being a huge fan of the product I really didn't give the situation the critical eye that I should have. Skip ahead maybe another two months and this time something that had been hanging for years fell off the wall in front of my eyes because the adhesive suddenly failed. I really don't know what to make of the situation, there wasn't any extreme weather that might have caused a problem and all instructions were followed when installed. My best guess is that the adhesive material dried out over time. Reading other reviews I see cases where the hooks fail after weeks or even months but not years. This product was still fairly new to the market when my pieces were hung; could it be that the hooks have a shelf life and will undoubtedly fail given enough time? Are the hooks only designed to last a certain amount of time before drying up or losing adhesion? I couldn't imagine one of these things for 50 years (something a nail should have no problem with), what about 20 years or 10? If the product has a lifespan that it's the manufacturers duty to inform us of that estimated lifespan even if it is multiple decades. I still have the problem of the nearly impenetrable walls and am extremely tempted to continue using them with the caveat that replacement will be necessary after 2 - 3 years and with an additional hook to backup the first one should it fail (which was what happened with the 2nd of the 3 failures I had). I don't want to say the product is totally useless because it's not, I just think it's important people recognize the possible shelf life that the product may have.