I think it means that we become accustomed to what we’re surrounded by. If you are exposed to/around something for a certain amount of time, that something becomes normal to you. It’s just like how everybody is part of a different culture, and some cultures practice things that may seem absurd to others, but it’s the norm for them. For example, if our society lived in a time where every single thing was electronic or vigils reality, then a child born and raised in that time would find that completely normal. They would have never known anything else.