The way that most quilters are taught to straighten fabric - bringing selvages together and sliding back and forth until the fold at the bottom is straight, then trim the end - does not really give you a true straight grain. It might be close, but rarely will it really be on grain.
Older members will remember learning to pull a thread, or on tighter weaves, to tear. Last year, while testing several brands of white fabrics, I tried pulling threads and found it to be nearly impossible. Quilting cotton is too tight to pull a thread, but too loose to prevent fraying. The reason I was testing the fabrics to begin with was bc I was so frustrated and annoyed with Kona cotton. Per Robert Kaufman, there is only one grade of Kona cottons, dispelling the common thought that they must have varying qualities for the big box stores and quilt shops.