It is what It is

After a long discussion yesterday with my almost 14 year-old brother about the truth and somewhat unusual comfort in the statement "You just have to let nature run its course," we argued how vague and unconclusional "It is what it is" is.  (yes I made up the word "unconclusional")

What exactly is "It?" And what "Is" it?

This is not a sufficient or comforting response to any situation!

Example:  

Boy: "A dragon just set my bike on fire! How will I get home from the disco party after school?"

Teacher: "Well...it is what is is."