My most effective hours are from 8-11am and 9-11pm. During those time windows, my brain is at its clearest. The problem with this reality is that much of the work day I am not at my "prime". 

As a professional, I have two choices in those less than productive periods. I could throw my hands up and cry "I'm not motivated" —or— I can choose a disciplined path and choose to make some contribution. These moments often reveal just how self-aware we truly are. 

We don't always have to be "on", but our productivity can't always be decided by motivation.