Xiuping Li at NUS Business School asked 80 students to write about a recent decision they regretted. Half of them were then told to seal their written recollection in an envelope. Afterwards, the envelope students felt less negative about the event than control students who just handed in their recollection without an envelope. The finding was replicated with forty female students who were asked to write about a strong personal desire that hadn't been satisfied.
Two further experiments shed some light on the process. Sealing a disturbing news story in an envelope reduced the negative emotional impact of the story and reduced participants' memory of it. By contrast, sealing an unrelated piece of paper did not have these effects, thus showing that it's the act of containing the emotional material that's important, not the mere act of putting anything in an envelope.
Finally, sealing in an envelope a written recollection of a regretted event led participants to feel less negative about the event than simply paper-clipping the pages together - so it's not just the mere act of doing something to a written recollection, it is specifically enclosing that material that is beneficial. What's more, this final experiment showed that the link between enveloping the material and participants' feelings was entirely mediated by their having a greater sense of psychological closure.
'We have shown that the metaphorical act of enclosing and sealing influences the memory, in the sense that the recollection of the emotional details of an event becomes weaker,' the researchers said. 'An effective way to relieve distress may be for the distressed person to seal an object related to his or her emotions in a package.' The researchers added that future research should test whether the effect still occurs if someone else does the sealing of the material, and if participants are told the purpose of the exercise.
Li X, Wei L, & Soman D (2010). Sealing the emotions genie: the effects of physical enclosure on psychological closure. Psychological science : a journal of the American Psychological Society / APS, 21 (8), 1047-50 PMID: 20622143