This passage from the essay Self-Reliance follows Ralph Waldo Emerson's remarks about people's reluctance to change their opinions that have already been approved by others. That is, people are disinclined to adopt new thoughts because they fear that new ideas may disappoint those who have previously approved of their others.
In his essay Emerson emphasizes the importance of thinking for oneself and trusting one's own thoughts:
The other terror that scares us from self-trust is our consistency; a reverence for our past act or word, because the eyes of others have no other data for computing our orbit than our past acts, and we are loath to disappoint them.
Emerson counters that this consistency is foolish because such rigid consistency in thought and action often prevents people from changing, growing, and developing their own potential. To be consistent is, to Emerson, as though the man were "clapped into jail by his consciousness."
Consistency of opinion and complacency in one's ideas and opinions is a terrible compromise of one's individuality, Emerson insists--"With consistency a great soul has simply nothing to do." There can be no growth or development in the person who does not change his thoughts. Further, Emerson encourages individuals to not be afraid to be misunderstood. He mentions that Pythagoras, Socrates, Galileo, and Newton all were misunderstood, along with "every pure and wise spirit that ever took flesh." In fact, Emerson concludes that "To be great is to be misunderstood...." because greatness looks to the future that no one can truly understand until later.