About tearing fabric.
In the "old days" fabric was manufactured a bit differently. As with everything else technology has affected the end result at the fabric plant. <G> If you remember those old cottons that were torn off the bolt, you had to iron them or they stayed a wrinkled mess.
Well, When "Permanent Press" clothes started appearing, the home sewists also wanted to be able to make clothing that didn't need real ironing, just the occasional touch up. So a "non wrinkle finish" was developed for fabrics. However, the "non wrinkle finish" also sets the grain of the fabric. It will return to the grain as it is set at the time the finish is applied. So, while we used to tug and pull fabric on the diagonal to straighten the grain, that doesn't work now. To "straighten" the grain of the fabric wash it and dry it. press as needed. That is how the grain will return when it is washed. Regardless of how much you tug it around.
Good things are not always totally perfect. <G> (By the way, one reason Home Dec fabrics are more expensive is that a lot more care is taken to make sure the grain is straight and perpendicular. That adds to the cost of manufacture, as do some of the extra finishes added to Home Dec fabrics. )
Have fun,
Pati, in Phx