If I have a better than 50% chance of getting the incorrect thing right the second time around, I will persevere. But I would never rip something out more than once or twice for fear of hurting the fabric! I would cut new pieces and do it again. If it is critical to the quilt, I would do practice pieces until I got the hang of it.
I do not see a big virtue to ripping things out so you can practice on them again and again. Cut yourself some slack or admit you need to practice a certain technique and then go back when you are ready. Relax!
