I'm confused about when jpeg files degrade.

I shoot photos in high quality jpeg format. Using a card reader, I download a copy of the whole card in jpeg format onto an external hard drive. They don't get edited or reduced---just copied. For processing, I download a second copy of the whole card in jpeg format onto my hard drive.

At that point, I review the thumbnails in the browse feature of PaintShop Pro 9. I may open a few of them, but I don't rotate them or do anything else. I delete any that are obviously bad. Then I do a batch conversion of the jpegs into psp files for processing.

Here are my two questions:

1. Once in awhile, I mistakenly save a change to the newly converted psp file. That's when I go back to my "negatives" to make a new psp file for editing. When I open and copy a jpeg file, is that an editing process? Am I introducing loss into the original or the new psp file that I make from it?

2. If simply copying a jpeg file does not introduce loss, what's wrong with keeping my "negatives" in jpeg format? They sure take up a lot less space.

Thank you very much for any insight you can offer.