Comment by mitchtbaum

If your battle with invaders happens inside your home, then you have only one more misstep before game over.

"When asked whether it would be prudent to build a defensive wall enclosing the city, Lycurgus answered, "A city is well-fortified which has a wall of men instead of brick."

https://en.wikipedia.org/wiki/Laconic_phrase

"It is said that if you know your enemies and know yourself, you will not be imperiled in a hundred battles; if you do not know your enemies but do know yourself, you will win one and lose one; if you do not know your enemies nor yourself, you will be imperiled in every single battle."

https://en.wikiquote.org/wiki/Sun_Tzu

Moral: https://en.wikipedia.org/wiki/Code_signing + https://en.wikipedia.org/wiki/Web_of_trust + https://en.wikipedia.org/wiki/Quality_assurance