They wouldn't be good for you if they weren't. And books that are over your head weary you unless you reach up to them and pull yourself up to their level. It isn't stretching that tires you, but stretching unsuccessfully because you lack the skill. The more you keep awake while reading, by sustaining the activity of asking and answering questions, the more exciting you will find the process. Don't be afraid that it will become too exciting.
Intellectual insomnia is still quite a long way off.
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