In less than 10 percent of cases the sleeve fails due to anatomical issues, poor surgical technique, or other issues that are no fault of the patient. Also, a tiny percentage of unfortunate souls have no favorable markers of chromosome 15, rendering them nonresponders to bariatric surgery.
Nonetheless, 90 percent of sleeve failures are due to the person failing the sleeve (e.g. behavioral issues).
http://thebodyimagecenter.com/wp-content/uploads/2016/03/why-we-hear-so-many-stories-of-failure-after-bariatric-surgery.pdf