Believing New Thoughts

Intellectually, I am understanding more & more the process of changing thoughts. But I am still having a hard time with believing some new ones. I understand that all thoughts are optional. I have a choice, yet it is easy to find logical proof to support that belief system involving thoughts of “not enough” in some ways.

My brain is trying hard to take me away from progress in this area. I know it is trying to protect me. I also know it is not helpful to believe those thoughts, but there’s all that “proof”.

Will you please share here about changing those self-defeating thoughts and really believing something different?

What are the fundamental things to keep in mind when dealing with things such as feelings of not enough, comparisons, others’ responses toward us, the victim mentality?

Thank you very much.