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What's something you used to do/see/say but don't anymore because you don't feel it's right?
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I respect your intuition to drop problematic phrases but you may have been lead astray on "rule of thumb" by a very common rumour (Wikipedia calls it 'modern folk etymology') that that is where it originated.
In fact no law ever existed and it was more used in trades as thumbs were an easy mode of measurement available to anyone (similar to the use of feet to measure!)
https://en.m.wikipedia.org/wiki/Rule_of_thumb
The Wikipedia article even explains the "switch" rumour and provides some backstory and explanation to it.
So don't feel weird using Rule of Thumb; it has more to do with carpentry than anything else.