Three good ones
For 'default' I tell people the computer or software program has made an 'assumption' about what you wanted ... and we all know what happens when you 'assume'; ass-u-me!
The next two are for anyone working on large projects, writing software, DBs, web-sites, etc. and the question arises 'why can't we just go back to what we had?" I tell them the 'project' is like a meal --you can't uncook a meatloaf. If the question is "why can't you stop where you are and finish later?", I explain "I'm in the middle of preparing a meal with all burners going. If I walk away now you will not like the result".