manual focus through the viewfinder (difficulties)

with general shooting in manual focus, are you guys relying on the green dot (nikon) feedback to determine if correct focus is achieved?  i'm a pretty advanced user, so i'm aware of diopter settings and everything that affects viewfinder and most focusing properties.

what's hard to grasp is that if i autofocus, get proper focus, and then slightly move the focus ring, the image through the viewfinder can look exactly the same, but the resulting photo is wildly out of focus.  just curious to understand how exactly manual shooters are able to discern when their focus is maximal.  are shooters able to tell when exact focus is achieved simply looking through the viewfinder?

thanks!