Viktor E. Frankl in Man’s Search for Meaning p. 88

[The] uniqueness and singleness which distinguishes each individual and gives a meaning to his existence has a bearing on creative work as much as it does on human love. When the impossibility of replacing a person is realized, it allows the responsibility which a man has for his existence and its continuance to appear in all its magnitude. A man who becomes conscious of the responsibility he bears towards a human being who affectionately waits for him, or to an unfinished work, will never be able to throw away his life. He knows the ‘why’ for his existence and will be able to bear almost any ‘how’”