We're perfectly capable of being bad enough at software to do that without invoking cosmic rays and quantum weirdness. How long would you expect to have to run

We're perfectly capable of being bad enough at software to do that without invoking cosmic rays and quantum weirdness. How long would you expect to have to run memtest on any desktop computer in good condition before you observe a memory error? Because I would expect the number to be somewhere between 'weeks' and 'forever.'