I think you need an additional component: no other desires except work. Many of us don't have jobs that fully satisfy (or let's be honest, even barely satisfy, since even 50% satisfaction would be nice and tolerable at some places) our minds, and once the thought patterns of "I can't wait for the day to be over so that I can X" start, they're hard to stop. Then you kind of need monk-like discipline to continually deny yourself your greater desires over the timespan of years if you don't want to go crazy / suffer burnout.