A desire path is a line that shows the most popular route, usually across a patch of grass. People want to get quickly to their destinations, so they cut corners.
In a busy city street, people are in a rush, to get home, to get to the shops, to get somewhere. So they take the line of least resistance....
But they cannot stop, they cannot give way. Once set on their path, they must get through. Like an oil tanker at sea, it can take miles before they can turn.
And when the do stop, they cannot move on. They block the doors of DLR trains, since those trains always stop in exactly the same spot!