Leeches are those review items that you always get wrong, and that just won’t stick. I think they’re called leeches because they leech your energy and time away for no good reason. Studying your leeches early on might be a pretty good thing to do. I think the self-study script has a mode where you can just focus on your leeches.
Also, I improved a little script that allows you to see your leeches and where they are.