Fall In Line Meaning

(idiomatic) To submit to the rules of a higher authority; obey; conform.

Example: 1901, Anna Maynard Barbour, That Mainwaring Affair, ch. 18:
  It will be to your interest to accept my suggestions and fall in line with my plans.
c. 2004, Career Soldiers, "Won't Waste My Life":
  If I had your life I'd put my throat to a knife,
  Fill your days with emptiness, but I don't have the time;
  I won't grow up, I won't fall in line.