Sonnet 29 is about a speaker who is initially downcast about his loneliness, but becomes happier when he thinks of a friend he loves. It is therefore about the reality of failure and loneliness mixed with the memory of happier times.
Sonnet 29 was written by William Shakespeare. He wrote 154 sonnets in total; this is part of the Fair Youth sequence.
It starts very resentfully and enviously, as the speaker talks about bemoaning his misfortune in the face of other people's success. But as it goes on it becomes apparent that the source of the speaker's bad mood is that he is not with a friend whom he loves. The bad mood is therefore driven by loneliness.
But then the speaker's mood starts to change. This is brought on by thoughts of the man he loves. He starts to feel happy and this then moves on to feelings of hope. The conclusion of the speaker is that despite his feelings of loneliness because his friend is not around, just thinking of him makes him feel good again. He even goes as far as to say that he would not change anything in his life: "I scorn to change my state with kings."