Use of only a single programming language considered harmful
Different languages allow us to think differently about problem solving. In psychology, the Sapir-Worph Hypothesis states that language influences thought (talking about natural or human languages here).
We spend a lot of time developing skills and acquiring knowledge based on programming experience. Some of that time should be spent learning additional programming languages. Have some fun - pick a new language like Ruby, Lisp, Smalltalk, etc. and program your brain in different ways to solve problems.
PS. the title of this article is obviously a tip-of-the-hat to Edsger Dijkstra and his 1968 article "GoTo Considered Harmful"