Especially when you don't have the first clue what center-body mass means.Pretty hard to shoot a charging Black bear center mass!
Here, let's see if I can explain it in terms even you can understand.
You see a bear. Your vision allows you to estimate what the borders of the bear's body are, from your point of view: sitting, standing, profile, head-on, whatever.
You approximate what the center of that area you see is.
That's where you shoot. Because you're scared, rushed, and your breathing and heart-rate are elevated. You will not make a dead-on-the-line shot. Shooting center-body mass allows you to miss your ideal point of aim, and still hit.
Of course, this applies to human beings, not all y'all cool, unflappable heroes of the paper mill.