The desire to constantly rise higher in the social sphere is the only motivation for action or movement in Vanity Fair. No character exerts effort unless it's in the service of finding a better-placed patron, campaigning for a new position, or acquiring a new status symbol. Those who plateau in their journey upward or who never really have the desire to elevate themselves become stagnant, boring, domestic people whose lives are secondary to the thrilling adventures of the strivers.
The world of the novel portrays all ambition (even seemingly innocuous ambition like the desire to marry or have a family) as necessarily having a sinister and selfish side. At the same time, there is no alternative offered for how to satisfied with one's position. This creates a very dark vision of humanity indeed.
The most determined character in the novel is Dobbin, who attempts to love and woo Amelia without distressing or bothering her in a way that would be ungentlemanly. His ultimate commitment to his own integrity in a sea of people who don't even know the meaning of the word is deeply optimistic and surprisingly ambitious.