A few hawk-eyed royal observers recently noticed a subtle-yet-intriguing detail about Meghan Markle and Kate Middleton: Both royals almost always appear in public holding their purses in their left hands. For real—take a look:

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And it turns out there’s a very practical reason for it. Myka Meier of Beaumont Etiquette told that the whole bag-in-left-hand thing is due to basic etiquette: You hold your purse on the left so that your right hand is free to shake hands and greet people—which is a huge part of one’s royal duties. She notes that male royals do the same with briefcases.

Honestly this is a genuinely useful pro tip (and we can’t believe we’d never heard about it before). Thanks, ladies…your style never ceases to inspire.