Here's a little story:

During a long and particularly harsh winter, a woman gathering firewood in the forest finds a wolf lying by the side of a path. He is starving and bleeding from a wound on his side, and looks to be on the brink of death. Because she is a kind woman who could never turn her back on anyone or anything in need, she picks him up and carries him home. She feeds him and bandages his wounds and nurses him back to health, and for weeks, the wolf would lay at her side by the fireplace, letting her stroke his head as he slept. Sometimes, he would lick her hand affectionately to show his appreciation and love. She became used to the wolf and even loved him, as her unconditional kindness had created a bond with this wild animal and had made him her gentle companion. One morning, she awoke to find her door open and the wolf was nowhere to be found. Deeply saddened, she searched the surrounding woods and left food out on her doorstep every morning in hopes that he would return, but he never did. She never saw him again and the abandonment by her lost friend broke her heart.

Does this story seem sad?

Here's the story from a different perspective:

During a long and particularly harsh winter, a wolf can not find enough food to feed itself. Starving and wounded from fighting for prey, he drops to the snow-covered ground, wheezing out what he believes to be his last breaths. Through his half-closed eyes, he sees an old woman approaching from the distance. The wolf knows that if he had more strength, he would rip through this woman's neck with his teeth and take her down. But in his current state, this is impossible. Luckily, the woman is a kind woman; she takes him home and nurses him back to health, sharing the food off her table with him and bandaging his wounds. The wolf greatly appreciates this woman's kindness. He lays by her side at night, and accompanies her during her foraging expeditions, loyal and protective. But deep down, something gnaws at him--he knows he is still a wolf and his nature is to kill. As his strength increases day by day, he begins to feel his predator urge creep up on him, particularly at night, when the woman lies sleeping in bed, her vulnerable flesh exposed. The wolf can not deny his nature even if he wanted to. Knowing this and because he loves her, one morning, when the door becomes unlatched by the wind, the wolf leaves, going back to fight for his survival in a harsh winter landscape rather than risk letting his nature hurt someone who has extended such kindness.

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I came up with this story as an analogy to describe an understanding of a recent/not-so-recent experience (take your pick) which I won't go into detail about. I figure, if you have been through this kind of experience, then you will understand the true meaning of this story. If you have not, then just take this as a story.