You study wrong.

There was a great interview about study habits and the debunking of some of the accepted wisdom. There were several obvious ones like "cramming doesn't work." By "doesn't work" it isn't that you can't cram for a test and pass the next day. What is meant by cramming not work is that there will be an incredible loss of content that evaporates from your memory fairly quickly. What you should do instead is break up learning over the longer term, quizzing yourself. Another piece of advice that I found particularly fascinating is that you should not only break up study by subject, but also break up the study within a subject, moving from area to area. For example: in a foreign language maybe you should practice a little on learning verb conjugation, then vocab, move on to something else. Long periods of studying just one thing will be counterproductive.

Take a listen. It was a very instructive and eye-opening segment.