To throw oneself into strange teachings is quite dangerous.
攻乎異端,斯害也己。
Original text (Chinese)
Source, in full
Note: The word translated "strange teachings" means literally another end [of textile]. There are two different understandings about "strange teachings" or heretical. One possible understanding is "strange from the authentic teaching", another understanding is simply different subjects, just as two authors or two scholastic fields literature and politics.