The following text will create a file with the lines broken correctly.
`Twas brillig, and the slithy toves \\
Did gyre and gimble in the wabe; \\
All mimsy were the borogoves, \\
And the mome raths outgrabe.
However, if you add the double backslashes to the last line, you will get an underfull hbox error message. That means that there is too much space on a line, i.e., the last line LaTeX sees is actually empty.