Fear of actually having what you want. Let me go into greater detail:
Not having what you want is an excuse to not succeed. People can be so interested in not having a good life or a joyful life that they self-sabotage their own interests with doing what it takes to not succeed.
Quitting fills the need for certainty. You like certainty so much that you quit only to prove to yourself and others that you can not stop your struggle with depression.
Comfort where you are. You have done depression for so long that you are comfortable and secure in it. To deal with life in another way is a change that you fear.
Certainty in not getting what you want. You want to fill the need for certainty or comfort so much that you will sacrifice joy to make a point.
I get it. I was the same. But when I made the effort to change I found it to be so worth it. How I did it is available here:
https://lylcoach.lchlegacy.com/