I change my needle often now, I didn't use to but with my newer Pfaffs it seems to fix the problem most of the time. Just last week I was starting a new project and put in a new needle, started sewing and the needle feel out. Reinserted and tighten and retighten the needle and it fell out again. Got out my tool that came with the machine to help insert said needle and retighten again and needle fell out. Got another needle out and inserted and worked perfectly. I can only assume that the first needle had a weird defect of some kind, that needle went into my used needle bottle never to see the light of day again. Lesson learned is that even a new needle can be a bad needle.