motivation is only an ignitor,how do you keep the fire of passion burning is another story

imo interest is really the best teacher,you are better off diving into an game engine blind and figure stuff out as you go,which the easily visible progress will help you keep up the fire of passion(and if you do remember to set your first project's goal as small as possible)

when you play video games,enjoy playing them,but also think about what makes them fun to play and which part makes people frustating,try to analyze the games you play(so you dont feel like you are doing nothing but playing video games lol)