Behavioral activation (BA) has come to be recognized as an empirically supported treatment for depression. Despite the general success of the approach, many patients experience treatment failure. Based on behavioral models of depression, we present several reasons for treatment failure in BA, including patient inability to understand and adopt the treatment rationale, lack of awareness or ability to articulate and behave according to life values, behavioral noncompliance, and ineffectiveness of contingency management to increase exposure to environmental rewards and reduce contact with both aversive environmental events and reinforcement of depressed behavior. A case study of treatment failure with a depressed breast cancer patient is presented, along with recommendations to reduce failure rates in BA.