I use an external usb drive to move some files. The first time I wanted to remove the usb drive, I just pulled it out. I got a message saying that was wrong. I need to use the eject button in Finder to avoid ruining anything. (not the Mac exact warning words). Next time I wanted to do the correct thing, but the eject is grayed out. Pulled out the same usb and got the same message. What am I missing here? I am new to Mac, so I know I am missing something.