When you realise you haven't taught them right
My husband bought me a new can opener it's great it leaves both the lid and the tin with a safe blunt edge.
Nathan wandered into living room with can of tapioca pudding and a spoon saying that openers great you can eat straight from the tin. As he munched his way through the lot.
I've failed, I thought I'd bought up a young man that used cutlery and crockery !
Heathen