The spec can be wrong for many reasons:

1. You can write a spec that builds something that is not what you actually wanted

2. You can write spec that is incoherent with itself or with the external world

3. You can write a spec that doesn't have sufficient mechanical sympathy with the tooling you have and so it requires you to all spec out more and more of the surrounding tech than you practically can.

All of those issues can be addressed by iterating on the spec with the help of agents. It's just an engineering practice, one that we have to become better at understanding

And what is a spec other than a program in a programming language? How do you prove the code artifact matches the spec or state machine