There is a great article on Macleans.ca titled "The powerlessness of positive thinking - Self-affirming statements actually make some people feel worse". The article presents research supporting the thesis that positive thinking is not as effective in improving self-esteem as some popular self-help authors would like readers to believe. I fully agree with the researchers that "focusing on positive thinking" is not the way to increase self-esteem or become happier. I believe that this is because a positive affirmation addresses the present, whereas the low esteem or tendency to think negatively is rooted in the past, usually the deep past.
Personally I've seen my self-esteem increase with the use of PBSP, about which I've written in an earlier post. And I believe that the reason PBSP works is precisely because it deals with self-esteem or negative thinking at the time when the roots of the issues begin - usually between the ages of 0-3.
Returning to the article, I do not agree with the researchers' statement that "...if you can find a loving, supportive partner that’s probably the best possibility for your self-esteem". In fact, I think that's a bit of a dangerous statement because that would make one's self esteem conditional on something, or someone, else. And like happiness, I believe you can't have self-esteem dependent on anything outside of yourself. In addition, increased self-esteem because of a partner could also lead to all kinds of co-dependency issues in a relationship, as per the Drama Triangle, also discussed in an earlier post.