This poem points towards the source of good poetry being a deep dissatisfaction that abides within the soul, which expresses itself in some of the most exquisite lines in all love poetry. The speaker in this poem writes, as he himself acknowledges, "the saddest lines" because he loves his love but has lost her, and he is faced with the torturous memories that he has of their time together and the feelings of sadness at grief at the end of their relationship. Note how he links his ability to write with the end of their relationship:
Tonight I can write the saddest lines.
To think that I do not have her. To feel that I have lost her.
His dissatisfaction involves both thinking and feeling, and it is this union that allows him to create the words of this famous poem that is such a powerful expression of love, regret and grief at the end of a relationship. The way in which both short sentences in the second line of the quote above powerfully leave the reader hanging, feeling the poignant emotion of the speaker, has an immense impact on the reader as it helps to communicate the depth of the speaker's sadness and despair.