you shift your d line strong side...and he runs weak side.
you pinch your d line...and he runs outside.
you spread your LBs...and he runs up the gut.
When you make shifts, he can see them and will adjust accordingly.
What to do? Disguise your run defense!
example 1: instead of "pinch d line" you "crash d line in", it will have the same effect without tipping him off.
example 2: you shift your d line strong side, and he runs weak side, only this time you have a weak side blitz coming. Boom!