The way I look at it, even if not self-contained (which I've done many times), it does translate to real life in a way. A lot of people will have explored the woods around their hometown growing up, and ventured into the next city. If you look at it from a fantasy lens, of course the person is going to know the area around the beginning really well, but not know much about the next place they go.

It's completely fine to make the start area hyper-detailed and it gets sparse the more they venture out. Once the characters are on the world stage, they care not what happens in the little forest outside the keep if they are worried about two rival kings going at each other's throat.