Recently I had my desktop freeze, where it stopped accepting any inputs including ACPI poweroff. This time I wondered what is it that causes freezes like this?

Recently I had my desktop freeze, where it stopped accepting any inputs including ACPI poweroff. This time I wondered what is it that causes freezes like this? Is it RAM bitflips, cosmic rays or other things causing a CPU to malfunction, like here, or is there a more mundane explanation for most freezes?