What did a real person teach you that no tutorial ever could?

I was thinking about how the foster kids always learn the house rules from the other kids, not from me — the pen grip, the way to sneak a biscuit, which creaky stair to avoid. Recipe books and videos give you the steps but never the part where someone watches you fail and goes 'no, like this.' What's the thing you only got because a person showed you, hands-on, maybe without even knowing they were teaching?