Like so many discussions on this site, people tend to over simplify. If X then Y. I have seen as many if not more passionate athletes that don't realistically have much chance of playing in high school let alone beyond. It's as sad to me to see the anger in the parent of such a player as the disappointed parent whose player doesn't share thier passion. Motivation is / can be the byproduct of several elements. It would be interesting to be able to formulate a few of the predominant algorithms that lead to success using the following elements.
Size
Personality
Athleticism
Aptitude
Experiences (good and bad)
Opportunity
Familial support
Socioeconomics
Geography
Popularity/Looks
Character/Integrity/selflessness
And I am sure there are others. It's our job as parents to manage, equip, direct and guide our children to achieve the very best/most given all the elements they've been blessed with. How we motivate or develope motivation is the real question of this thread. I love the suggestion of building a love for the game.