In casual conversation, people experience little psychological discomfort in admitting that they have some particular character flaw, but only if they consider trivial the flaw to which they admit. Ttherefore, if in a casual conversation an individual readily admits that he or she has some particular character flaw, the individual must not consider that flaw to be serious. Which one of the following is an assumption necessary to the argument? ['People admit to having only those character flaws that most other people consider trivial.', 'In casual conversation, people readily admit to having a character flaw only when that admission causes them little psychological discomfort.', 'In casual conversation, people admit to having character flaws only when they must.', 'Most character flaws are considered trivial by those who have them.']