Experience is Useless without Reflection
To live a life that shall be entirely prudent and discreet, and to draw from experience all the instruction it contains, it is requisite to be constantly thinking back, to make a kind of recapitulation of what we have done, of our impressions and sensations, to compare our former with our present judgments - what we set before us and struggle to achieve, with the actual result and satisfaction we have obtained. To do this is to get a repetition of the private lessons of experience, lessons which are given to every one.
Experience of the world may be looked upon as a kind of text, to which reflection and knowledge form the commentary. Where there is great deal of reflection and intellectual knowledge, and very little experience, the result is like those books which have on each page two lines of text to forty lines of commentary. A great deal of experience with little reflection and scant knowledge, gives us complex books where there are no notes and much that is unintelligible.
The advice here given is on a par with a rule recommended by Pythagoras - to review, every night before going to sleep, what we have done during the day. To live at random, in the hurly-burly of business or pleasure, without ever reflecting upon the past, to go on, as it were, pulling cotton off the reel of life, is to have no clear idea of what we are about; and a man who lives in this state will have chaos in his emotions and certain confusion in his thoughts; as is soon manifest by the abrupt and fragmentary character of his conversation, which becomes a kind of mincemeat. A man will be all the more exposed to this fate in proportion as he lives a restless life in the world, amid a crowd of various impressions and with a correspondingly small amount of activity on the part of his own mind.
Arthur Schopenhauer, in 'Aphorisms for the Wisdom of Life'