The short version: morning cortisol levels peak between around 8-9am. Coffee consumption during peak cortisol production periods mean you get less of a buzz, and develop more of a tolerance/addiction. So one possibility: it's best drinking coffee outside of the periods of the day where your cortisol typically spikes. This is all very confusing to me and I'm going to pour a cup of coffee and watch it again.
From ASAP Science, by Mitchell Moffit and Greg Brown. They have a book.