Quote Originally Posted by bmccasland View Post
I just want the left strap to not fall off my shoulder....
That's often postural.

The lower trapezius, rhomboids, and middle trapezius on one side aren't doing their job; and/or the ribcage is turned slightly and the sternum is dropped. No matter how you adjust the strap, the dang thing slides off because the shoulder is diving out from underneath it.

On me it's my right shoulder. Drives me nuts. (especially because I know why it happens but I don't *want* to have to correct my posture, dangit! Though the strap stays up if I do...)