oh. it's metaphorical, and probabaly means different things to different people. (i think it's what's commonly called "ART HOUSE")
for me it's about having the power and determination to go against the grain.
to finally achieve enlightenment. the ability to look at what you want, then look at those around you, and make a desision that you want to be more than this. then you start your journey towards that end.
i see the big people at the start as being the enlightened ones, their higher stature shows they have a different and perhaps more knowing way of looking at the world (as only a higher vantage point can provide).
the guy sees them, envys them, and starts to notice that everything is going backwards, he tries to go against the grain, getting violently thrown back a few times by teh backlash of his environment (including social envioronment). but he perceveres, he keeps picking himself back up. he gets more fluid in his persuit, amazing some onlookers* as he runs past.
(*did you notice that the only people who took note of what he was doing were children
. the pure characters who learn from everything, and most in touch with their inner selves.)
until eventually he's running so fast, and he launches himself with all his power at the walls to his existance. he breaks through, and achieves his goal. now he walks among the taller ones.
then he notices a child looking at him. just as he himself was looking at one of the taller ones at the start. and the child then starts to walk against the grain - just as he did. she starts to travel down his path, then the filmclip ends, so her spiritual journey is then up to your imagination. will she make it as he did?