This topic seems to be about cognitive dissonance and the success or futility in one's chosen way of settling the discomfort. Cognitive dissonance is the stress that occurs when beliefs, feelings, and perceptions contradict in some way. Common strategies to relieving cognitive dissonance are rationalisation, confirmation bias, and perhaps thought suppression.
Beliefs and feelings are distinct phenomena. Beliefs stem from experience and inference, and are semantic in nature. Feelings stem from fitness of beliefs, needs, wants, and fears with perceived or hypothetical circumstances, and are emotive in nature. If some belief or feeling has been suppressed, it may resurface in the form of cognitive dissonance or intrusive thoughts. This is especially likely when under high cognitive load. Another place suppressed thoughts are likely to show is in the content or theme of dreams -- a phenomenon termed dream rebound.
The negative experience described in the question results not from the belief itself, but the fitness of the belief with something else -- likely another belief, desire, or perception. For example, if one believes that only persons with type X body are attractive, and one perceives oneself as lacking this body type, then one may experience mental discomfort.
One thing to consider is the origin of the belief -- in this case the belief that only body type X is attractive. If one can trace back how it came to be, one may no longer hold it so tightly. In practice, many beliefs come about through socialisation, or taking in the norms of society, family, and other circles. Sometimes, as was given in the example in the question, a person may choose to identify with a different subgroup or selection of people, so as to procure a different set of cultural norms against which to compete.
There are of course cases where a belief may itself be irrational. This is particularly common in anxiety disorders, but it may also occur in cases of delusion or body dysmorphic disorder, among others. Such belief can be especially troublesome to overcome. If the belief stems from an underlying pathology, treating the illness may help to bring clarity. One popular treatment method is cognitive behavioural therapy. This may help to resolve irrational thought patterns, or cognitive distortions. Another method is cognitive restructuring, which seeks to reappraise and reformulate automatic thoughts through rational rebuttal.