Tangent: Imagining a positive event never happening makes us appreciate it more

"In Studies 1 and 2, college students wrote about the ways in which a positive event might never have happened and was surprising or how it became part of their life and was unsurprising. As predicted, people in the former condition reported more positive affective states. In Study 3, college student forecasters failed to anticipate this effect. In Study 4, Internet respondents and university staff members who wrote about how they might never have met their romantic partner were more satisfied with their relationship than were those who wrote about how they did meet their partner."

Source: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2746912/