Start from how people actually behave, not how they ought to behave.
Machiavelli says many writers describe an imaginary ideal state. He wants the real one. A ruler who plans for how people should act gets destroyed by how they do act.
how one lives is so far distant from how one ought to live, that he who neglects what is done for what ought to be done, sooner effects his ruin than his preservation
Chapter XV · Concerning Things for which Men, and Especially Princes, are Praised or Blamed