Oh, so I say that Haiku and old Chinese poem are 2 beautiful flowers with the same background. Their common root should be based on the traditional Chinese theory named "天人合一" originated from Zhuang zi庄子 and developed by the confucian scholar 董仲舒whose doctrine has a huge influence to China: the theory that man is an integral part of nature. It emphasizes the harmony between man and natuere. So Haiku and old Chinese poem both focus on the natural scenary. I just check the information about 贾岛 and it shows that his poems are noted for describing the desolate and bleak (荒凉枯寂Wabi-Sabi) scene. No wonder I feel Haiku comes across as a kind of tragic esthetics.

Thank you for telling me that 贾岛 had a big influence to Basho. (I have learned that Wabi-Sabi is just one of 6 characteristics of Haiku. )I must say I seldom read 贾岛’s poems, and I don't think that he was as popular as 李白,杜甫，as well as 王维/Wang Wei and 白居易,etc. in China. I only know one of his poems. Now I've realized that that poem really has an atmosphere of Haiku being called Yūgen (幽玄). Maybe I can share it later. It is really so interesting for me to know 贾岛's poetic soul has pervaded into Japanese Haiku!