Traditional Culture Encyclopedia - Photography and portraiture - Why is the selected part blurred instead of the unselected part when taking shift photography with photoshop?

Why is the selected part blurred instead of the unselected part when taking shift photography with photoshop?

It is suggested to copy a layer, then blur it, then create a mask for this layer, and then draw a clear position with a soft black brush.

Recommend a relatively simple software, alien skin shot, depth of field plug-in, the effect is quite good.