When C does what you ask it to do, you're probably just getting lucky. It's more or less impossible to write a nontrivial C program without relying on undefined behavior.
With the exception of the translation limits (a strict reading of which may allow a compiler that can only compile a single program), it's pretty much trivial to avoid undefined behavior.
Implementation-defined behavior can be harder to avoid, but that's not a problem if you're targeting a known implementation.
