All in a days work

I've been studying off and on all day for 12 hrs. I can't study (ok maybe I shouldn't say.can't) I prefer not to study for long periods. of time because I tend to lose focus and forget. I'm proud of myself because I did what I dId I was going to do. So now I'm done for the night. I'm not going to force myself to study when I know I won't retain anything.