What's the basis of cognitive behavioral therapy?

Thoughts matter: The fundamental idea behind cbt is that our interpretations of events affect our emotions and behavior. Thoughts, behaviors, and emotions are interconnected. A change in one of these aspects of our experience influences the others. With cbt, dysfunctional beliefs and negative automatic thoughts are replaced by more functional beliefs and thoughts. As a result we feel and behave better.

Sphere of influence: We have little to no direct control over our emotions and our physical reactions. However we have a high degree of control over what we think and in my opinion almost 100% degree of control over our behavior. If we see the relationship we can effect change.