For old times' sake
Back in the day, PCs had no hard drive and an OS like MSDOS or CP/M had to be loaded from floppy disk on startup.
Neighbour had an Amstrad PCW. The main program for it was the Locoscript wordprocessor, which was integrated with a modified CP/M so that the whole shebang booted off a single disk: clunk, click, whirr, and you were away. You could also get other programs, such as spreadsheets, which ran on CP/M.
Talking one weekend, he says he's bought a spreadsheet but it won't run, so he'll have to send it back on Monday.
I offer to take a look, he shows me the PCW and the offending spreadsheet disk.
I ask, "have you got the CP/M floppy which came with the machine?"
"Somewhere probably, why?"
"You need to load the OS before programs can run on it."
" * "