NAND flash is prone to bit flips – cells that are not meant to be accessed during a specific read or write operation can change contents due to read and write activities in adjacent cells or pages.
Read Disturb: A read disturb occurs when a cell that is not being read receives elevated voltage stress. Stressed cells are always in the block that is being read and are always on a page that is not being read. The probability of read disturb is much lower than is a write disturb.
Write Disturb: A write disturb occurs when a cell that is not being programmed receives elevated voltage stress. Stressed cells are always in the block that is being programmed and can be either on the page that is programmed (but cell was not selected), or on any page within the same block.
So anyway, I was reading about this because I wanted to understand better what leads to picture and video files fucking up on a USB flash drive seemingly randomly. I understood that a great number of rewrites to the same cell wears it out (so to speak), but that would not explain why a stored file that was good would later turn to shit. I also understood that in any case, cells leak electrons so that eventually the charge state is degraded too much. But since that is supposed to take years after the writing, I was not satisfied with that. So assuming the reputable brand has good standards and quality control, so far I am inclined to blame "write disturb", though am not satisfied to certainty.