Panta rhei

Everything flows - Heraklitus.

Well known fact; when you write down the specs, the world is changing. By the time you've finished the implementation the world is no longer the same. This why we all went agile.

There is another side to this; with an agile approach you take shortcuts in the first iteration. Most simple thing you can do, blabla bla. However a couple of iterations down the road, you forgot you took some shortcuts. People start cursing the whacky implementation, forgetting that this was a deliberate choice and now the time has come to crank up the implementations.

Iterations also pose a challenge for QA. In my experience they are still used to the waterfall process. It is hard for them; each iteration new functionality is delivered but still some things are not (yet) fully functional. The deliverable of each iteration has to be carefully defined to enable them to properly test the deliverable. However, how much time you are going to invest writing a detailed document that is obsolete after the next iteration? Worse, how are you going to get the full spec after all iteration are finished? How efficient are UI designers if they know that each iteration the UI will change? Do they start with a wizard or tab-based approach because they know the next iteration requires more widgets?

There is some kind of impedance mismatch between the development process (iterative) and the product as itself. As usual a trade-off.