Back in 1993, the band Little Texas released What Might Have Been, a beautiful song about a failed relationship and, of more importance, the folly of "knowing" how life would have changed had the breakup not occurred. The sentiments expressed in the song can be applied to many aspects of our lives.
Once we reach the age of independence, and sometimes before, we begin to make choices that determine the course of our life. These decisions relate to friendships, education, job opportunities, romantic relationships, lifestyle and career moves, among many others. As we age, we tend to look back on those choices and, too often, second guess ourselves, wondering if mistakes were made and if our life could have been better. Of course, this analysis is made in hindsight and is devoid of context; our imperfect memory, which tends to embellish happiness and suppress pain, fuels the uncertainty.
As the song suggests, we can't know how life might have been and we certainly can't change the past. But we can learn from our experience and we can always change life's present course (should that be appropriate).