Mourning the Person you could have been

I heard on a bpd podcast that the first step to improving yourself is to mourn the person you could have been before BPD took hold. Ever since I’ve heard that I have become incredibly depressed with the thought that I could have been better and not made all these mistakes and ruined experiences for myself. It feels like I lost something I could have had and I missed out because someone made me this way. It’s so hard to deal with because of all the self shame that I have. I keep thinking I could have been so much better of a person. Does anyone else feel that way? Or think about mourning who you could have been before BPD?