|Do you know where your variables are?|
Daily, and I just had my most recent "thank the maker" experience from that.
Thursday, I had backed up my laptop at 9am, to a bootable clone, as I do daily, every day that I'm home.
At noon, I rebooted my machine to finish the installation of something that wanted a reboot (rare on OSX, but it happens).
The reboot failed. Two hours later, with all the various attempts at fsck's and safe boot, it still wouldn't boot.
So, I booted from my external clone, and it came up (albeit slowly). After a two-hour "clone the external back into the internal" sequence, my internal is rebootable again. Yeah.
Thank the maker. I lost a couple of podcast masters that I had created in the meanwhile, but far better than losing months of work.
ALWAYS MAKE BACKUPS. DAILY.