As in the title, I'm looking for an expression/idiom where a novice tries to lecture an expert on their field of expertise.

  • Well, "mansplaining" comes close. – Hot Licks Sep 20 '18 at 0:22
  • That's a good specific example. Is there a more general term that comes to mind? – BonesVI Sep 20 '18 at 0:29
  • There are a number of metaphors (which don't come to mind just now), but single words are apt to be hard to find. – Hot Licks Sep 20 '18 at 0:43

teach grandmother to suck eggs

To try to teach an older person who is wiser and more experienced and worldly than a young person may think. Why are you explaining basic typing to Ethel? Yes, she's 70, but she's been using a computer since before you were born—quit teaching your grandmother to suck eggs.

Or, if you prefer:

teach fish how to swim

Teach fish how to swim is an idiomatic expression derived from the Latin proverb piscem natare doces. The phrase describes the self-sufficiency of those who know better how to do everything than the experts. It corresponds to the expression, "teaching grandmother to suck eggs".

There's also:

I've forgotten more than you'll ever know

but I am unable to find a reputable reference for it at the moment.

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