don't try to teach Grandma how to suck eggs
An older person is wiser, more experienced, and more worldly than a young person may think—thus, the older person does not need to be taught by the younger. I may be 70, but I've been using a computer since before you were born! Don't try to teach Grandma how to suck eggs, sonny! You young hotshots come in and try to prove you know the ropes better than we do—please. Don't try to teach Grandma how to suck eggs. Did it ever occur to you that I might already know how to do this project all on my own? Don't try to teach Grandma how to suck eggs.
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