the story shows us the human condition and relationships. Going through the endless journey everyone had a part of.
The neverending cycle of life.
For what reason, we are moving forward? we don't even know. All we know is that something will bound to happen during those times.
Should you...
I noticed that there are different kinds of people inside the bus. the author might be showing us the cycle of life itself, starting from the infant up to the old man.
I might be just over reading into it but since their topic always ends up in the meaning of 'life', I think it made some sense.