This is a very straightforward lecture, on the topic of 2PC and 3PC. Students only find one aspect a bit tricky, which is the idea that even though 3PC (like 2PC) has "bad states" in any real setting (because of imprecise failure detection), 3PC is still able to make progress with higher probability because those bad states are less likely than the ones that can cause 2PC to hang. Students find this confusing for some reason.
It is worth mentioning that there are some kinds of systems where we have a failure detection module that we're told to trust. In these systems, 2PC can still hang, but 3PC would never do so.