The author Bai JuYi wrote this when he was only 16. This is his poem for a literary exam. The story goes that he took this poem from his hometown to the capital. He then show it to a recognized literary expert 顾况 Gu Kuang, so that he may publicize for him. Gu Kuang looked down on his age, and jokingly said “长安米贵，居大不易。”（京城里粮价高得很，住下很不方便吧。） This means that the grains in the capital is expensive and it would not be easy to stay there. This is a pun on Bai JuYi's name which means easy to stay. But after reading the line, "野火烧不尽，春风吹又生", which describes how the wild grass can never be burned out by wild fire, and grows again easily every springtime, he then exclaimed: “有才如此，居亦何难！”（能写出这样的诗句来，走到哪儿住下都方便得很！） This means that with such great talent, it is no difficulty to stay anywhere. This shows great affirmation on Bai JuYi's talent.
Indeed this line 野火烧不尽，春风吹又生 is a powerful one. It is a vivid description of the tenacity of nature (wild grass), and the persistence to survive another day. And this is why it is often used as a word of comfort to the downtrodden. An amazing line from a 16 year old indeed.