The way Windows copies files is incredibly annoying. When you copy a large batch of files, and an error occurs, Windows just stops and waits for you to tell it what to do, instead of continuing with the files it can deal with. Worse, if it runs into a corrupt file, it will just quit, with part of your stuff copied, part not.
When you have to re-start a copy of a large folder, you will obviously wind up with a lot of files that already exist. Windows asks if you want to replace the old file with the new one, and gives you options--Yes, Yes to all, No, and cancel. The most useful option here would be "no to all", but it doesn't exist.
...except I just found out it does, sort of. Hold shift while clicking "No" counts as "no to all".
I'm copying my music to my new work laptop, and waiting for Windows to show me the duplicate file error--I know it is going to, because I've already copied half my music before I had to leave for work. Perversely, it appears to be copying the files in a different order than my first attempt. I know it is going to complain about duplicates and wait for instructions, but apparently it is going to wait for me to go to bed first...