Every single thing I have read (or heard) that was written (or spoken) by a bariatric medical professional confirms that patient non-compliance is the most common cause of band failure. That failure can take many forms, anything from disappointing weight loss to serious medical complications. If you don't follow your surgeon's and nutritionist's instructions, don't return to your surgeon for follow-up visits and fills, ignore negative symptoms, don't change your lifestyle, and don't address the things that made you fat in the first place, you are setting yourself up for failure.
Despite careful patient screening, pre-op education, and post-op education, sometimes the band just doesn't work. This can be a function of unrealistic expectations, inability to make lifestyle changes, failure to participate in aftercare programs, and plain old bad luck. A solution is to revise to a different weight loss surgery procedure, but if you can't or won't do the hard work of following up with your surgeon and changing your behavior, you might be disappointed once again.