Comment by sunir

From a computer science point of view, it's the same argument as why NP-complete problems are hard to solve, and easy to check.

From a practical point of view, however, it's the same argument we write unit and integration tests. We accept error rates in the program under test, the test, the test harness, the programming language, the operating system, the hardware, and the universe. The goal is reduce the error rates enough you can ship something you can get paid for and won't get sued for later before you starve to death.