Why do people regret actions they didn't take when looking back on their lives?
The classic reference for exactly what you are describing is Gilovich &amp; Medvec, 1995 (LINK), the primary thesis of which is that "Actions, or errors of commission, generate more regret in the short term; but inactions, or errors of omission, produce more regret in the long run" (from the abstract). The authors explain that there are many factors that contribute to this general pattern; these factors are actually summarized quite nicely in their Table 3 below:


For a more complete description of these factors and a discussion of the relevant evidence, see the link I posted above to the Gilovich &amp; Medvec paper.

References


Gilovich, T. &amp; Medvec, V.H. (1995). The experience of regret: what, when, and why. Psychological review, 102, 379. PDF