Damage done by self-help books

Those who follow by blog closely would, by now, have noticed that I am not taken by the secrets offered in The Secret (see here, for example).

Now comes the news that self-help mantras can leave some people actually unhappy. People who are low on self-esteem will end up feeling worse when the repeat self-affirming statements. It works only for people who already have a a high self-esteem. This is based on the study conducted by Joanne Wood, John Lee and Elaine Perunovic.

Question: Why would people with high-self esteem want to repeat self-affirming statements?