There’s an old engineering rule about fast, cheap, and reliable – choose two. If you’re at NASA and you’re sending something to the moon you need it to be fast and reliable, but you can throw away cheap. Throwaway medical instruments in an operating room need to have a different thing – doesn’t have to work for long, and since you’re going to throw it away it would be nice if it’s cheap, so you make your trade-offs.

That as a rule of thumb is mostly what engineering is about. You can have most things, but not everything. I think security engineering are about tolerable failure modes – are about what the tolerable levels of failure are. Determine what failure modes are tolerable and what are not and I can design around not having the intolerable ones. But the cost of it will be some others, because you can’t have them all. So when I say, not not fast, cheap and reliable but freedom, security, and convenience, choose two – it’s in that spirit as an engineer.