It's only impossible when you look at rapidly developing, easy to use systems. Which is my point and why the broad assertion is wrong. Look at a VxWorks type

It's only impossible when you look at rapidly developing, easy to use systems. Which is my point and why the broad assertion is wrong. Look at a VxWorks type OS. Or OpenBSD. Limited capability and compatibility, very strong security guarantees. "Completely secure" isn't a mythical unicorn. It just costs time and money. A LOT of time and money.