Cognitive Behavioral Therapy (CBT) is a common form of psychological therapy and often regarded as the most effective. 

There are some criticisms of CBT and among them have to do with the research suggesting its efficacy. 

Reading Wikipedia, I came across the following statement that suggests that CBT studies have high drop-out rates:

Furthermore, other researchers[151] write that CBT studies have high drop-out rates compared to other treatments. At times, the CBT drop-out rates can be more than five times higher than other treatments groups.

It just seems likely that if a particular form of therapy has a high drop out rate, only the most dedicated to improve their condition will remain at the end of the study. And what needs to be said of dedication? Wouldn't we all agree that being dedicated to a cause helps us succeed?