The Holy Spirit within can be illustrated by the internal guidance systems that are commonly used by ships, planes and spacecraft today.  These vehicles all have an inner gyroscope that is based on the magnetic pull of the Earth.  A gyroscope sends signals to instruments indicating the attitude, or the position of the vehicle.  Pilots spend years, decades and thousands of hours training themselves to trust the readings given by the internal gyroscope, not outside reference points.  Many pilots have died overriding their instruments and depending on their human senses in a crisis situation.  The human eye and the inner ear particularly can give false readings leading a pilot to believe that they are in one position when actually they are in another. 

For example, in the dark with no visible horizon or outside reference points, a pilot can easily believe that he is right side up when he is upside down.  This is known as spatial disorientation.  If a pilot will choose to believe his instruments over his inner ear, he can pretty much be assured of safety.  The inner ear can give a false reading but the magnetic pull of the Earth, although it may vary ever so slightly at the poles, will never give a false reading.  Pilots are trained to trust their lives to this fact.

The human mind, outward circumstances, trusted loved ones, however well meaning, can all give wrong guidance that appears to be right, just like the inner ear of a pilot can.  The Holy Spirit, on the other hand, is like the inner gyroscope based on the magnetic pull of the Earth.  He will never give a false reading because His guidance is based on the pull of the Father Who is All Knowing.