Just finished Les Miserables (the book, not the musical). Lots of interesting reflections in there (and a great tale, too). In the final chapter the novel's hero, the Christ-like ex-convict Jean Valjean, after bringing about the happy marriage between his adopted daughter Cosette, whom he had saved from a miserable life and whom he has taken care of for the last ten years, and Marius, the man she loves and whose life he saved not long ago, allows himself to be cast aside, suddenly no longer needed and wanted when he tells Marius about his past. There are some misunderstandings, and Marius doesn't know that Jean has saved his life, while Cosette doesn't really understand what is going on, but given all that Jean has done for them, their behaviour still amounts to gross ingratitude. In the end they learn the whole truth, realise just how ungrateful they have been and try to make up for it, but before that happens, Victor Hugo, or his narrator, reflects on how grave the moral failure of the two ungrateful lovers actually is. And rather surprisingly he finds their behaviour, and generally that of young people, who tend to forget the benefits they have received from the old, not only excusable, but almost justified:
"what is sometimes over-severely described as the ingratitude of the young is not always so reprehensible as one may suppose. It is the ingratitude of Nature herself. Nature (...) always 'looks ahead'; she divides living creatures into those who are arriving and those who are leaving. Those leaving look towards darkness, and those arriving look towards light. Hence the gulf between them, fateful to the old, involuntary on the part of the young. The gulf, at first imperceptibly, grows gradually wider, like the spreading branches of a tree. It is not the fault of the branches that, without detaching themselves from the trunk, they grow remote from it. Youth goes in search of joy and festitivity, bright light and love. Age moves towards the end. They do not lose sight of one another, but there is no longer any closeness between them. Young folk feel the cooling of life; old people feel the chill of the grave. Let us not be too hard on the young."
So in other words, it is not only natural for the young to forget the good that they have received from the old, but it is also, for this very reason, right. It is exactly as it should be.