Core Beliefs

I notice from looking back in journals that I’ve been dealing with some issues for decades. The same thing over and over again. Then other issues that were recurrent, suddenly stop being an issue, and never come back. I’m trying to figure out the difference. It seems like in the later case, I’ve deleted a core belief, and so how did I do that? Is is the repetition of turning around limiting thoughts enough times that it finally sticks? Is it making a commitment or a strong decision? Sometimes I feel like I’ve repeated the same turn around a thousand times, and made a strong decision/commitment a thousand times, and yet the immature thinking is still there. Then with other issues it goes away forever. Any advice on why it works sometimes and not others?