We train our dogs for everything even when we are unaware that we are doing so. Conditioning a dog happens when we ourselves have a routine and our dogs follow along.
For example when we go outside we open a door. When we want to go back inside we open a door. Our dogs will watch this behavior over and over in their lifetime and we have hence condition or have taught the dog that to go inside or outside a door is opened.
The video below provides a humorous example when a door is no longer part of the inside/outside process dogs are so familiar with!
Video Source: Mert Burlock – Dogs & Imaginary Doors