Special?

There is a zen story about a master and his disciple crossing a river.
The disciple shows-off to the master by walking across the surface of the water.
The master wades through the water instead.
When he has crossed, the master says to the disciple: "If I'd known you were going to perform a miracle, I'd have broken both of your legs."

What does this story mean?Zen is not something special.
It is not an image, label, badge or adjunct to your personality.