You do have to talk back to those negative thoughts. You have to work hard at it, but you must at least try to "think a better thought" and not succumb to the futility or allow those thoughts to suck you further into the muck. Recognize that those thoughts are also symptoms of the depression and are NOT indicative of who you really are.

One of the things I had to do was design my own "measuring tape" because I too had always believed that I was a failure in meeting other people's expectations. I realized that in the end, we and we alone are the creators of our own lives, nobody else. So the only person who gets to measure my worthwhileness and success is ME! Other people will force their opinions and expectations on you, but you and you alone get to decide who you are and how you want to live - there comes a point in our lives when our mothers no longer get to decide who we are and who we WANT to be. The truth is that you can be whoever you want to be - you get to make that choice, and there is NOBODY out there who can make that choice, or gets to judge your choice or you. It's YOUR life, YOUR self, YOUR choices to make.

You will HAVE to talk back to those tapes, and begin rewriting them with what YOU want to hear yourself saying to yourself - and be generous, because in reality, whether or not you can see it right now, you ARE a noble, wondrously incredible being with infinite possibility (and it's entirely up to you which of those possibilities you want to chase after and become). The core truth of each one of us is that we are ALLOWED by God, by the universe, by our deepest selves, to be anything and all that we choose to be. If those old tapes are getting in the way, rewrite them so that they don't get in the way - rewrite them so that they open doors and windows to better possibilities instead of keeping you locked in that nightmare of self-imprisonment. Nobody has the power anymore to keep you there - you can rewrite your way out of that darkness, one word, one thought, one step forward at a time.

The other reality is that nobody else CAN do that for you. Therapists will help us find that way, or the motivation, or the courage and will companion you along that way out, but you are the one who will have to make the choices that will actually get you out - and those choices begin with talking back to those old tapes which are no longer valid (probably never were) and are NOT who you are...you get to decide who you are - and reach for the stars when you decide who you are, because you are infinitely greater than you can possibly imagine.
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When you don't like a thing, change it.
If you can't change it, change the way you think about it.

(Maya Angelou)