What if I'm so used to quitting that I never reached stage 4? What if I never had anything I care about finished? What's the way for me to reset my mind on the matter?
Then you are not interested in what you are trying to do. You really don't want to solve that problem. So get interested. Internet is your best friend here. Reason out WHY do I need to do this? And convince yourself why. If you are not convinced that this problem is important to you, you are never gonna do it.
You're right. The thing is that I'm terrified of success, because reaching it might mean that I might fail, and that'd be hurtful, so I often convince myself to do something that can't possibly hurt me instead... like eating a lot of sweets or sitting my ass off in front of the screen. Human mind is an amazing thing, but sometimes it lays path to Hell with its good intentions. But laying it off on my mind is shifting responsibilities. I'm the person responsible for how I perform; whether I succeed in an achievement that's more than internal is not entirely up to me, but what I can - and must - do is do my best. I am interested, and I must also remind myself of that, and of that it's better to fail at achieving goals than to not try. Thank you for reminding me of that.