The pervasive sin in Little Dorrit is excessive, usually unjustified pride. It is a psychological state shared by the majority of the characters, and it is always a hindrance. How so? Well, characters with too much pride have difficulty forming emotional connections with those around them. They often react in a huff to anything that happens, rather than taking reasonable actions. They also have trouble valuating the people and situations they come across accurately. And, ironically enough, their overweening pride prevents them from conducting themselves in a manner that could turn them into the kinds of people who could justifiably be proud of themselves and their accomplishments.
The social hierarchy of the novel rests entirely on people being able to maintain overly inflated opinions of themselves in the face of evidence to the contrary. Just as the Parliamentary satire shows Circumlocution Officers blithely spewing meaningless but impressive-sounding self-congratulations, so in private, the elite spends most of its time complimenting itself.