We go down with the size of the transistor, so the insulator of the floating gate is getting thinner and does not create such a potential barrier to effectively prevent the escape of electrons. We pack more and more bits into smaller and smaller transistors, so we have to distinguish more and more charge levels. As a consequence, the difference in the content of the floating gate at the level of 100 electrons translates into a bit error. Smaller transistors are also more densely packed - this translates into problems related to electrical induction. In addition, we produce multi-layer systems, which means that we have to struggle with heat dissipation from the center of the systems, and induction does not only apply to neighbors in 2D, but also in the top-down system. The systems overheat especially during write and erase operations that require voltages approx. 20 V. As a consequence, the service life of new circuits is much lower than that of old ones. At the moment, the entire information storage logic in NAND chips is based on much more extensive and advanced correction codes than it was 10 years ago. If you are also unlucky and come across a manufacturing defect, you buy a corpse that is unusable from new.