Psychological scientists seldom ask such questions, let alone investigate them empirically. One exception, however, is Shige Oishi and his colleagues Ed Diener and Rich Lucas. These three researchers set out to establish the optimal level of happiness in various domains of life. What they found was intriguing. When it came to social life and social activities - for example, the likelihood that one is in a stable intimate relationship, has a good number of close friends, or does a lot of volunteering - the happier, the better. Those who scored a "10" on a 10-point happiness scale were the ones who reported the most success when it came to their social and romantic lives. However, when it came to how much money people made, how well they did in school, or how politically active they were, it was the moderately happy group (i.e., those who scored approximately an "8") who were the most successful.
So the optimal level of happiness turns out to be "as high as possible" when it comes to relationships but "moderately high" when it comes to work. Being deliriously happy all the time at the office may not serve our productivity very well (and might drive our colleagues to avoid us). However, apparently, we prefer our friends and spouses to be extremely happy. A line of research on idealization in relationships is consistent with this view, showing that the most satisfied couples are those whose members see one another more positively than they really are.
It's not surprising then that marriage and family therapists routinely teach couples to think positive thoughts about each other. For example, in marriage counseling, you might be encouraged to explain your husband's misdeeds in charitable ways (e.g., "He only screamed at me in front of the neighbor because he'd had a trying day"), and you might be discouraged to count how many times this week he criticized or snubbed you. Unfortunately, this kind of therapy isn't effective for approximately 50% of couples.