I was using 'motivation' and 'desire' as synonyms, not contrasting one with the other. Desires change, so therefore actions change.
Desires aren't mutually exclusive, but the point I was making is that when your desires change so do your actions, and therefore so does the effect. For example, you can try to go north and east at the same time, and end up going north east, but each step north east doesn't take you as far north as the same step would if you were heading directly north.
It is always difficulty that provokes improvement. There are many ways to face difficulties that do not involve competition and losing.
If you're working with a team, competing against other teams, then it's not the competition part that helps you learn to work with others, it's the cooperation with your team members. Doing two things at the same time doesn't mean that they are both the cause of any effect you see.
If I create a game that involves shooting people while reading a medical book, does it follow then that guns help treat illness?
The shift from internal to external I was referring to is the change from internal motivation to external motivation. As a matter of fact, I think parkour is largely internal. The only external part is the obstacle, whereas the difficulty, the desire, the method, the solutions and the improvement are all a part of you.