An ungrieved loss remains forever alive in our unconscious, which has no sense of time.
Dr. Charles Whitfield, one of the recognized therapists of the "Child Within," once wrote, "An ungrieved loss remains forever alive in our unconscious, which has no sense of time." From that vantage point, we can see that past losses or even a reminder of them tend to superimpose upon current losses, thus evoking greater intensity of fear or other negative feelings in us. I call these "frozen losses" which keep us stuck.
In summary: "Past losses and separations have an impact on current losses, separations, and attachment. And all of these factors bear on fear of future losses and our capacity to make future attachments" (Simos, 1979).
Because grief is such an overwhelming event in therapy/recovery, I only know of one way to begin to heal - identify and process the ungrieved loss/es. It's the start of getting free of its painful hold on our selves and lives.