C.N+vain

http://www.merriam-webster.com/dictionary/vain

It is key that you, the reader, know the word **vain** because if you do not understand the word while reading the poem then you would not be able to comprehend the message in the line.With the correct definition of the word you can translate the line to mean " When it is safe for you to try to dodge it". I chose the picture below because it shows a man dodging a bullet to protect himself and helps provide a visual representation and explanation for the phrase "When it's vain to try to dodge it".