Listen to your process feedback
Paraphrasing an overheard conversation,
"This agile process is creating all sorts of problems for us. We are finding all sorts of problems that we wouldn't normally find."
"Oh. Wait. They were always there, weren't they? We just never realised..."
All agile processes are designed around regular feedback. They try and touch all phases of delivery as soon as possible, forcing issues to the surface early before they become too damaging. The process is designed makes problems visible regardless of how uncomfortable this may be. They are an unforgiving mirror on the reality that we are often too close to see.
But visibility is only the beginning. Just because something is visible does not magically change it into something better - it just means that you know it is there. To change something requires a conscious effort. Your success or failure depends entirely on how you react to the information you are provided with. This reaction has very little to do with the process, and more to do with improving the way the team is working. Denial is not just a river in Egypt....
Or in other words, agile process is only as effective as the people using it. It is entirely dependent on your reactions to the feedback it provides. A failing agile process says much more about the adaptability, reactiveness and maturity of the organisation using it than the process itself.
To put it yet another way, you will never be agile if you refuse to be agile.