I recently lost a chunk of data while I was developing a nice little macro to produce a report. How it was lost, is pretty sad. I had become used to pressing a few keys to clear out my spreadsheet, and I accidentally pressed the keys on a spreadsheet of the live data. Pffft. Data vanished.

I luckily had most of the data in another document, and restored some of the lost data, but, the lost bits were lost. All this was due, not to faulty code, but because I failed to create a development sandbox.

Yes, this was only a macro, but, even for something so simple, it's smart to make a separate place to develop it. This sandbox would have contained a copy of the data.

A sandbox is better than a backup. That's because the sandbox is a minimal subset of what you need to write your program. The real deployment environment is usually a lot more complex. To back up the real environment, so it's safe to develop in there, could be more difficult than you could imagine, and take a long time, too.

I tell everyone "work on a copy of the data, not on the original." Well, "physician, heal thyself," is what I should be told. I needed to work on a copy of the data, and not the original.