yeah, but we don't double check the calling/return of every builtin and we don't double check our double check, recurse. There can be bugs in the OS, or networ

yeah, but we don't double check the calling/return of every builtin and we don't double check our double check, recurse. There can be bugs in the OS, or network driver. Life happens. At some point you have to assume something works bug free. A common and reasonable point for that is "I assume language and builtins to actually work as documented".