(IME - 2010/2011 - 1 FASE)An old axiom says that i

(IME - 2010/2011 - 1ª FASE)

An old axiom says that in order to know where you are going, you first have to know where you are. To that, add that you should know which way you are facing. Makers of wireless handsets, proving the old axiom true, have already installed Global Positioning System (GPS) receivers, and are now poised to flood the market with phones containing tiny electronic compasses that allow the gadget to sense exactly what direction it’s facing. 

What general idea underlies the paragraph?