Stop studying what you know.
Candidates are happier when they are reviewing areas that they know well.
Once you enter a difficult area that has been a weakness in the past, the comfort level with the topic drops dramatically. Use this drop in comfort level as a clue. You are weak in the area and you need to work until you can correct some of the weaknesses. Yes, there is too much information to work until you know everything perfectly. There are not enough hours in a day to do that.