Most DONMs have a core belief that they're never good enough. And in truth, you probably never were, are, or will be good enough for your narcissistic mother. Because such a thing doesn't exist. She makes it her business that you're never good enough for her, because she likes to make sure you keep trying. She wants to keep you off-balance, and weak and vulnerable, and feeling off-centre.
You know the image of the donkey and the carrot: the point is that no matter how hard the donkey tries, it'll never reach the carrot.
That's us, and the carrot is our narcissistic mother's approval. Oh, she might give us approval rarely and minimally, to keep us in the game (casinos know this - you need to have occasional wins to keep 'em hooked). But that approval will be taken away as quickly as it was given. Don't want you getting complacent and comfortable now!
The problem is that she gave you that 'never good enough' message, and you took it on board and internalised it and made it part of your own truth.
This is totally understandable - it's absolutely NOT something to beat yourself up over. In other words, don't start feeling not good enough about the fact you believed you weren't good enough.
She was your mother, and all children are programmed to totally look up to their mothers and believe them. Why would you not?
Also a lot of this 'never good enough' message was unspoken and subliminal and so went straight to your subconcious. The message was given in deep sighs, and rolled eyes, and heavy silences.
Those messages are very profound, and for a child, impossible to protect yourself against.
The good news is that once you've recognised the whole Narcissistic Mother thing, you can conciously recognise that those 'never good enough' beliefs aren't true. That's huge.
But it's not enough. Those beliefs are very deeply engrained. And unfortunately, carrying around those beliefs affects your behaviour, and affects how you treat yourself. So they're important to remove.
One way to remove them is explained in the page on Negative Self-Talk.
However the quickest, easiest, and most powerful way to remove them is through the use of EFT/Tapping. EFT literally reprogrammes your beliefs, taking out all those 'never good enough' feelings and replacing them with a quiet confidence.