Preparing for the California Bar Exam was a fascinating experience for me. Not only was it the most mentally challenging endeavor I had ever undertaken, it proved to be the most psychologically challenging as well.
Fortunately, our two bar prep professors were not only licensed attorneys, but also Ph.D.s in neuropsychology. Part of our rigorous training therefore was not simply learning the law, but actually learning how to learn -- in particular, how to store and recall so much data on demand -- and above all, how to manage our time. (It turns out the human brain is actually quite good at writing and storing data, but really bad at what can be best described as "random access memory" operations: recalling random data at will, instantly.)
A great deal of emphasis was placed on structuring extremely precise "living schedules," for example, what to study when, for how long, when to eat, what meals, and above all, how and when to sleep. And how to force ourselves to sleep when we couldn't.
Long story short, forcing ourselves onto regular sleeping patterns was both immediately necessary and yet proved to be one of the hardest disciplines to learn: to force yourself to stop studying at a given hour (typically 10PM) even in the midst of learning something, and allow time to drive home, have a snack, rest, unwind, and then fall asleep by 11PM, to then awaken at 7 and be back at the library at 8... every single day, for 2 months... that was truly an act of willpower. Especially for me, as I've always been the personality type where, once I start doing or learning something, I can't stop until it's totally finished or mastered. Forcing myself to stop studying without having yet completed the particular matter was excruciatingly difficult.
The same thing proved true for the three-day bar exam itself of course: had to sleep between 9 and 10PM and awaken by 6AM, with virtually no studying at all in between days. At this point, you just had to trust your brain to marinate on all that it had absorbed in the 2 months leading up to those fateful three days.
Looking back on it now, it was due largely to my discipline with sleeping habits that I was able to pass the bar on my first try.