What are the similarities between characteristics of a person and a guitar ?

I assume you're being asked to think creatively here.  If
I had to come up with points of similarity, my first one would be that both a guitar and
a person need the right amount of tension to perform correctly.  A guitar will not sound
right if the strings are tightened too much, but it will also not sound right if the
strings are not tight enough.  You can argue that people are the same.  If we have no
tension in our lives, we have no urgency and we are not likely to work hard and fulfill
our potential.  If we have too much tension, though, we are likely to fail because we
cannot handle the stress.

I suppose the other similarity
could be that all of our parts have to work together for us to function properly.  When
you play a guitar, you have to hold all the strings in the proper way for each chord to
sound right.  The strings all have to work together (not to mention what your
strumming/picking hand has to do).  In our lives, all of our "strings" have to be "held
right" as well.  For us to function at our best, we have to have our work life and our
personal life and perhaps our spiritual life all working
correctly.