We don't put up our home address on the Internet because we don't want random strangers to find out where we live.

Some others, we don't open the compound gates for and interact with them from outside. 

Fewer still, we let in through the gates and perhaps into our houses, but we don't open up our private spaces inside the house to them.

Maybe a couple of people have a spare key to our house. 

We clearly define the boundaries for these people.

We protect our mental spaces with similar boundaries. We are selective in what we share with whom about what we're thinking and what we're feeling.

The problems start when we don't have a clear understanding of where the boundaries are and do the hard work of honouring them.