I mean they’ve tried and recently, but there are actually a lot of additional problems that kick in as soon as you try it e.g. you can’t just use the air for fuel for oxidiser once you are going at the sorts of speeds you need to achieve.

Skylon (spacecraft) - Wikipedia https://en.wikipedia.org/wiki/Skylon_(spacecraft)

Other good options

“Is it a boy or a girl”

“Yes” / “One of those” / “Almost certainly” etc

What if your compiler is compromised? https://www.cs.cmu.edu/~rdriley/487/papers/Thompson_1984_ReflectionsonTrustingTrust.pdf

It depends on the level of mistrust you’re willing to entertain but the short version is; no, you cannot be sure.

Ken Thompson’s 1983 talk, Reflections on trusting trust is the classic talk on just why you cannot be sure.