My Ah Ha! moment came when I started PP using Carol Doak's method of PP'ing. I got to a point where I was spot on every time. She offers a great deal of information and patterns on her web page,
https://www.caroldoak.com/about.php . I now lay the pieces about 1/2" larger than the pieces I am piecing and then trim after stitching. I was pretty much a lost soul before being introduced to her method.