Motivation? F* Motivation! Great things are achieved through discipline over time. Discipline is destiny not motivation. 
Discussion
If you do the thing that suits you personally (morally),
motivation will be a consequence of what you do, keeping you going seemingly without effort.
Discipline can make you better if you apply it to form a routine around what suits you, otherwise it will destroy you (burnout) over time.
I have had the dicipline to support the wrong thing (ethically right, morally wrong) over 20 years and with a moral mismatch this resulted in an inevitable burnout.
Be wise, don't be me (in this case 😅)
My tip for the day:
Keep an eye out for when you end up being in "flow".
Chances are that what you were doing motivated you, you lost track of time and it matched some of your moral values. 👍
For some personalities, discipline is freedom.
For other personalities, freedom is their discipline.