“Letting go” sounds much more physical than it is.
It is a change of perspective more than a change in actions. It is viewing something not as part of the controllable present anymore, but as part of the unchangeable past. It is believing that nothing can be done about it, and if there was, it should not be done now. It is an acceptance that what already happened is all there is, and all there will ever be. The possibilities, that were hoped to happen, become understood as vacuous; they were possible only in the sense that they did not contradict the laws of physics. In hindsight, only facts are important and possibilities mean nothing.
Although it can be hastened, it cannot be delayed. Time dilutes everything, eventually. The pain that you should feel as long as your loss stands will be taken away, carving more helplessness into an already weak structure. Not only to fail, but to be denied the ability to truly “appreciate” every detail of that failure. The pain that remains is a general one. An indistinguishable pile that was formed by failures of the past, only larger by a degree of one failure. Immovable, and continuously growing. Once, it seemed to be a reasonable price for everything else. Now, it has pushed everything out and it is all that can be seen. Troubling to deal with, and too troubling to ignore.
A distinction has to be made between failure as a cost of learning and failure as an unchangeable characteristic. A characteristic that continues to define every new memory.