Isaiah Berlin says:

"When the natural road towards human fulfilment is blocked, human beings retreat into themselves, become involved in themselves, and try to create inwardly that world which some evil fate has denied them externally.

If you cannot obtain from the world that which you really desire, you must teach yourself not to want it.

If you cannot get what you want, you must teach yourself to want what you can get.

This is a very frequent form of spiritual retreat in depth, into a kind of Inner Citadel, in which you try to lock yourself up against all the fearful ills of the world."

@robkhenderson explained it in a simpler way:

"If your leg is wounded, you can try to treat the leg. If you cannot, then you cut off the leg. And announce that the desire for legs is misguided and must be subdued."

Basically - if you can't win at a game, you stop playing, say that you never cared about that game and create your own game with rules which you can more easily win at.

This psychological defense mechanism reveals both the resilience and tragedy of human nature. We possess an extraordinary ability to adapt our desires to our circumstances, but in doing so, we might be cutting ourselves off from genuine aspirations and authentic growth.

The Inner Citadel can be both a refuge and a prison - protecting us from disappointment while potentially limiting our willingness to persist through challenges or seek creative solutions to overcome obstacles.

Source: Chris Williamson