A NPR article questions why we don't actually magically start singing in the middle of the street like they do in musical. After all, it should make perfect sense if the whole idea behind singing in musical is expressing what words simply are not big enough to express. There are plenty of places in life where I'm sure we could use a different form of expression than simply language.
That is where music comes in.
Quite literally - this is when we turn to art; whether it is theatre, musicals, music, novels, poetry, or painting, we need something to communicate a larger emotion or shared experience. Sadly in our modern society art is not a common form of this expression. We tune into the television or log on to the internet. All of us have our own personal soundtracks that follow us where we go in our iPods. We don't need to come up with the words ourself because we can simple look them up from someone else.
If you were to write your own soundtrack, what would it sound like? What is your inner monologue? What are those things that are difficult to express because you feel them so deeply? You may not be the one to write a play about them - perhaps you can find the expression in an existing work of art and there is nothing wrong with that - but what is your voice in all of that?