Basically it's that memory changes out from under you. As we know, computers use Binary, so everything boils down to it being a 0 or a 1. A bit flip is changing what was say a 0 into a 1.
Usually attributed to "cosmic rays", but really can happen for any number of less exciting sounding reasons.
Basically, there is zero double checking in your computer for almost everything except stuff that goes across the network. Memory and disks are not checked for correctness, basically ever on any machine anywhere. Many servers(but certainly not all) are the rare exception when it comes to memory safety. They usually have ECC(Error Correction Code) Memory, basically a checksum on the memory to ensure that if memory is corrupted, it's noticed and fixed.
Essentially every filesystem everywhere does zero data integrity checking:
MacOS APFS: Nope
Windows NTFS: Nope
Linux EXT4: Nope
BSD's UFS: Nope
Your mobile phone: Nope
ZFS is the rare exception for file systems that actually double check the data you save to it is the data you get back from it. Every other filesystem is just a big ball of unknown data. You probably get back what you put it, but there is zero promises or guarantees.
Usually attributed to "cosmic rays", but really can happen for any number of less exciting sounding reasons.
Basically, there is zero double checking in your computer for almost everything except stuff that goes across the network. Memory and disks are not checked for correctness, basically ever on any machine anywhere. Many servers(but certainly not all) are the rare exception when it comes to memory safety. They usually have ECC(Error Correction Code) Memory, basically a checksum on the memory to ensure that if memory is corrupted, it's noticed and fixed.
Essentially every filesystem everywhere does zero data integrity checking:
ZFS is the rare exception for file systems that actually double check the data you save to it is the data you get back from it. Every other filesystem is just a big ball of unknown data. You probably get back what you put it, but there is zero promises or guarantees.