Cathexis is the investment of mental or emotional energy in a person, an object, or an idea.
So decathexis taking that energy back. (Thank you Henry Cloud, for this explanation in Necessary Endings).
I have been familiar with the concept, but not the term – at times in life, you have to MOVE ON; and in order to go forward, that means saying good-bye to something else – something that is currently alive for you in some way, but probably should be put to rest.
For example, the kids who do the best in college (emotionally) have to let their high school experience go, and actively invest in their new environment and friendships. Part of what helps a new marriage thrive is that changing of allegiance from parents to new spouse.
It's not just relationships that this concepts plays itself out it. Often, as people engage in new jobs or entrepreneurial exploits, at some point, one can no longer sustain both. In order for the new to succeed, the old has to be curtailed. You give your notice and now put full effort into the new thing.
This concept even holds true with ideas. In order for you to become at peace with the parent who never engaged with you much, you have to let go of the expectation that if you just tried harder, they would come around and give you the love and attention you desire.
If you think of energy as a budget item and you evaluate how it is parceled out … what action, idea, or relationship needs to have its energy allocation withdrawn, so that that impetus can be invested into something new ?
And, oh, by the way, letting go is a form of death. Decathexis always involves grief. And that's an entirely different blog post.