Most of us carry fixed sentences, declarations that stand in for our picture of ourselves: I always ruin things at the last minute; everyone will leave me; I can't take pressure. They feel like facts because they have been repeated so often - but repetition is not evidence, and not one of these declarations has ever faced a real trial against the evidence. This theme is a hearing, held over several days inside your optimistic writing.
You don't have to side with whatever contradicts them. Try to be a fair judge and look at the evidence. You will probably see a great deal that runs against those sweeping generalisations - whose origin you don't even know, and which paint you in the colour of failure, or weakness, or of not being trusted.
The verdict you write after each day's evidence will be nothing like a simple sentence. Even if you find that you really did "ruin some things", you will never be the person who "always ruins things". Gathering evidence and writing daily gives you the detail instead: "in the cases where X happened, I found that I'm liable to fail because I don't like working under those conditions, and I found that a little more effort made me succeed. And I found that in most matters and with most people I do the opposite of ruining things, and I have heard good words from everyone about it."
Leave the file open. A belief that took years to settle will not vanish in one evening; you will write about it for a while, a line or two each day, and life will not stop producing new evidence. When the old sentence gets loud again, come back to the writing, add what happened, write again, and call up the memories in which you found that belief to be entirely wrong.