I am a philosophy student and I have noticed that there are some days (rarely) in which I simply can not absorb. A lot of times I will work extra hard to concentrate but find that it is simply useless and a waste of times. Is it necessary to take breaks from intellectual work? I always just assumed the mind could handle whatever you could feed it, is this false? Are there things in which I can do to improve my concentration and productivity in situations like this? Or do I just need to slow down?