everything follows law of nature.to master this law,you need to think,which requires peace.and to maintein this peace,you should be alert to the outside evironment.coming at this point,you need at least two clues of concern for the sound living,to think and to guard(to judge),you gotta have enough brain room for these,to think and to judge. nature is full of thinking instead of judgements and fighting.as it goes,the sleep is the best thinking for it comes from nature.