Pontiac Montana SV6 2008 Owner's Manual page 32

If you slid under it, the belt would apply force on your
abdomen. This could cause serious or even fatal injuries.
The shoulder belt should go over the shoulder and across
the chest. These parts of the body are best able to take
belt restraining forces.
The shoulder belt locks if there is a sudden stop or crash.
Q:
What is wrong with this?
A:
The shoulder belt is too loose. It will not give nearly
as much protection this way.
1-28
CAUTION:
{
You can be seriously hurt if your shoulder belt
is too loose. In a crash, you would move
forward too much, which could increase injury.
The shoulder belt should fit snugly against
your body.