Comment by rob74

And because you have sprints, you create lots and lots of small tasks, then focus on them, and then team members forget the "big picture" of how everything should fit together in the end (if they were ever aware of it). And when all of those small tasks are done, you notice that the sum of all those parts is not what you set out to build initially, and you need more time to shape it into something that resembles what you wanted to have.

To avoid this scenario, it takes really dedicated project managers, product owners and lead developers, and not everyone has those...