The team/organization has to become a learning organization. That means a number of things, but the critical one here is learning from past failures and successes and incorporating that feedback into their model (ideally continuously, but in Scrums it'd be the end-of-sprint retrospective). You start down a path, and you find it's difficult. You don't press on just because it's the one you selected, that's the way of idiots. You examine the hardships you're facing, and you address them.