How does MIRI Know it Has a Medium Probability of Success?

In the past, people like Eliezer Yudkowsky (see 1, 2, 3, 4, and 5) have argued that MIRI has a medium probability of success. What is this probability estimate based on and how is success defined?

I’ve read standard MIRI literature (like “Evidence and Import” and “Five Theses”), but I may have missed something.


(Meta: I don’t think this deserves a discussion thread, but I posted this on the open thread and no-one responded, and I think it’s important enough to merit a response.)