The easy way to alleviate this potential problem? MAKE A COPY OF THE PROGRAM (or whatever) YOU HAPPEN TO BE WORKING ON AND MESS AROUND WITH THE COPY!! This isn't a hard thing to figure out. How long does it take to make a copy of a file? Usually less that a minute or two. It's time well spent. This way, if you accidentally waste whatever you were working on, you can always go back and try, try again. This is bound to happen with a program like ResEdit, especially if you really get into experimenting with things.
Intuition:
Remember: the Mac is the most "user-friendly" computer in existence today simply because it works in a way that many people are already somewhat used to and can readily adapt to. The Mac uses what's fancily called a Standard User Interface, which means in English that (usually) functions such as Open, Close, Print, and Quit are to be found under the File menu; Undo, Cut, Copy, and Paste are located under the Edit menu; the way you scroll a window is the same in MacWrite as it is in the Finder, Excel, or anywhere else; procedures for selecting text do not vary from program to program, etc., etc...
