It is very easy to rely upon shape, size, sound or location of something when describing it. For example, "click on the green button" assumes that the user is able to perceive colour - which they may not be able to do if they are colour blind. "The items in the left column are for sale" assumes that the user is able to perceive location - which they may not be able to do if they are blind and using a screen reader. By providing descriptions that do not rely upon a particular sensory perception, this ensures that instructions can be understood by everyone.
Build in some redundancy by drawing upon multiple properties of an object when you describe it. For example, changing the instructions to "click on the green arrow labelled 'next'" and "The items in the left column headed 'Sale Items' are for sale " should ensure that they can be perceived by everyone.
No example is available.