It is a stability concern. If every substituent on a chair conformation cyclohexane was axial upwards, there would be clutter and steric strain. It is not as energetically favorable as alternating axial bonds up and down.
First of all normally students use that in hexagons and their boat structures.
So, Basically the common mistakes are that they never try to visualise things. Because equatorial bonds are perpendicular to visualised plane and axial bonds are kind of in plane. If you once get this thing visualised, all your problems are over with these bonds.
and if you are having problems in visualising things you can contact me on my email (#hemantkadyan#@#gmail#.#com#).
If you contact me I can also arrange a phone meeting where it will be easy for you to get things in your mind.