This.
Being able to say “We tested 40,000 hammers and only 1 of them broke the very first time we used it” is not the same at all as saying “You can probably use this hammer 40,000 times before it breaks.” MTBF is more like the former. They connect 1,000 hard drives to a testing machine and run it for 2,000 hours. If they get one failure halfway through the test, they can say the MTBF is 1 million hours. But that’s not nearly the same thing as running a single drive continuously for 1 million hours (114 years), let along powering it up and running it for one hour then powering it down again 1 million times. I doubt that anyone in their right mind seriously thinks a hard drive can possibly still be working 114 years after it was built.