A metaphor is a figure of speech that is used to make a comparison between two seemingly different things in order to describe an object or action. In this quote the route we fall in is compared with a beaten track.
The idea is to better describe the particular routine.
This quote is a metaphor because it is describing something as something else here it says we fall into a particular route and make a beaten track for our selves, it is not actually what it says but because it does not say the word "like a" we know it is a metaphor since it is ensuring unlike what a simile does.
