Have you yo-yo'd then found success?

Hello! I have been trying to lose weight for a long time. I gave birth 18 years ago and since then I have lost a little, then gained, over and over again. I've never hit my goal weight. I feel more motivated now and I am trying to set up healthy habits. But my problem is that since I've never achieved my goal weight, I worry that I never will. I say I have tried to lose weight for years, but the truth is that I'll lose 10-15 lbs, then give up. Then I start again and lose the same 10-15. I want to lose at least 40 lbs. I've never even lost enough to see a small difference in the mirror. Looking at these success stories, it seems like people just one day decide to lose weight, and they do it. I guess I just need some encouragement and someone to tell me that my body and mind are capable of actually following through. And if you have stories of yo-yoing for years and then finally following through and meeting your goal - that would be encouraging too! Thank you all in advance.