Since I made my adages post last year, I've had a few afterthoughts, so here's a second instalment of things I seem to find myself saying a lot.
I'll start with a more or less frivolous one, which I tend to think of as the Law of the Kitchen: in a kitchen there's nowhere safe to stand, or perhaps no matter where you stand in a kitchen, you're in someone's way. This applies in any kitchen that more than one person is trying to use; no matter how spacious it appears, the one place you pick to try to stay out of the way is inevitably going to turn out to be right in front of the cupboard somebody needs. An office building I used to work in had an absurdly large kitchen, and I still saw this happen all the time. The only way to avoid it is to be alone in the kitchen, and sometimes I think even that doesn't work reliably.
There's a sentence that I always wish I'd put into my old article ‘How to Report Bugs Effectively’, because it makes a nice one-
Also on the theme of computer (and other) troubleshooting, a phrase I shamelessly pillaged from Yes, Minister and adapted slightly to make it work in a totally different context: if you don't tell me exactly what you're doing, I can't tell you which bit you're doing wrong. I often find myself saying that to people who email me asking for detailed advice without giving enough details of their own, and it usually seems to get the message through.
Continuing the topic of user-
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If you're trying to persuade people to do one thing rather than another, a thing I've come back to a few times now is that it's better to make the right choice easier, not the wrong choice harder. (Because either action provides an incentive to switch over, but one of them also makes people's lives better whereas the other makes them worse, so it will make a big difference to how annoyed with you they are afterwards.)
An argument I've used a few times to persuade people to actually bother to start backing up their electronic data is to point out that backups are a kind of housework. They actually are, if you think about it: things like hoovering and bathroom-
As before, of course, none of these should be taken as a universal truth or applicable in all circumstances, and all of them have their implicit ifs and buts and unlesses and exceptions. Caveat lector.