does python have useless destructors?

[Roy Smith]

> > Maybe I don't need it, maybe 310 gives me RAII and that's what
> > I really need.  I don't know, but again, 310 doesn't give me
> > anything of consequence in terms of software architecture.

I just read PEP-310, and there's something I don't understand.  It says:

>     Note that this makes using an object that does not have an
>     __exit__() method a fail-fast error.

What does "fail-fast" mean?