Because, on Sunday morning, all the icons for Office disappeared, along with Adobe stuff, Evernote and a couple of other apps, document icons too. I've seen this happen in earlier versions of Windows, so I wasn't too bothered - just need to find the location of the icon cache, delete it and let the OS rebuild it. Which I did. And it didn't.
I turned to Google and MS Answers and lost an hour understanding the HUGE number of possible causes and resolutions. None of which worked. Gave up on it and resigned myself to reinstalling the affected apps, starting with Evernote and Adobe, both of which recovered their icons. Then I turned to Office, once I'd dug the installations disks out from some dusty corner of the attic - and that's when the fun really started. Installing over the top of the existing installation failed halfway, with a meaningless error. Uninstalling - I wish I'd never decided to do it - failed halfway with another meaningless error, but got far enough to have removed the apps. Installing over the top of the now useless installation failed with... you get the gist. Lost another hour filtering error messages out of the Windows Event Viewer, Googling them, throwing them at Technet, all to no avail.
No other route open to me: I'm now in the land of 'format c:' and reinstall the OS. I keep all the data on a separate partition - but have to reinstall all the BLOODY apps, find all the latest BLOODY drivers, re-instate all the BLOODY user accounts, add back in all the BLOODY BITS OF CONFIG, set up all the BLOODY backup jobs again. Etc. Etc. I started at 11pm on Sunday evening and went to bed at gone 2am, with a clean Windows install, the latest 110 Windows patches applied, MS Defender watching for infiltration and some remote access software in place (the excellent TeamViewer). Left it plugged into the network and went to bed.
And on Monday I dipped in when I had a moment at work and kicked off the occasional installation, jobs to rescan all the pictures, find all the music etc. I'm still tweaking bits now, two days later.
Which brings me to the one useful bit of advice out of all this. I don't know how many times over the years I've had to do this with an OS, but more than I care to think of. I've always been anal about backing up data, but backing up data is not the same as backing up the core OS, the apps, all the little tweaks you make over the years... And for years, it's been quite possible to do that, you just have to invest a bit of time in creating an image of the OS partition. Every time I've been through this I resolve to do exactly that - and I never get round to it.
Not this time. This time I am now the owner of a shiny image of the rebuilt system, clean as a whistle, which I can re-instate at the click of a clicky-thing - and, moreover, not just to the same hardware, but to a completely different chunk of tin, should I need to.
If you've ploughed your way through all this and wondered where the payback is - well, that's it.
For no money at all you can go and research the wares at easeus.com, download them, spend half an hour understanding them and then use them. I guarantee someone will be saved tears - of frustration, if not loss - as a result.