You either do or don't
Basically saying do it or don't,it just matters on what happens on one of those choices. If you or someone else is not really wanting to do something, but at the same time you technically can do that thing, that's where the phrase "You either do or don't" comes into play.
Example 1: Someone that works can get up to go to work, but they don't want to, if someone else says or that person remembers the phrase "You either do or don't", they will think about the outcomes of either decision, therefore proceeding with one of the choices depending on how they want it to play out.
Example 2: Have better eating habits to better your health or keep up bad eating habits and then your health declines
Example 2: Have better eating habits to better your health or keep up bad eating habits and then your health declines