[re: variables] One of my favorite words in the English language.
I can't say it's a favorite word, but it's certainly a concept I cherish and embrace.
Even if the following from Donald Rumsfeld was being used, illegitimately, to brush away responsibility for something he had a central role in, the actual concept itself is absolutely valid:
"
As we know, there are known knowns. There are things we know we know. We also know there are known unknowns. That is to say, we know there are some things we do not know. But there are also unknown unknowns — the ones we don't know we don't know."
And, it's usually either the selectively ignored "known knowns" or the "unknown unknowns," which cannot be planned for, that really come back to proverbially bite us in the tush in the worst possible ways. There seems to be more consistent contingency planning for "known unknowns." (But, let me be clear, you can get bitten in the tush by any of the above if you do zero planning.)
And when it comes to OS maintenance, for your average user or even your average tech, there are way more "unknown unknowns" for us than there are for the people who developed, and are tasked with maintaining, any given OS. Just as it would be foolish to tell your doctor that his advice is foolish, and you'll listen to social media instead, it's equally foolish to believe you know more about what does, and does not, need doing as far as the "care and feeding" of any OS than the people who make it do.