What is a saying for "a bookish inexperience preaching the experienced"

Question

Like Preaching to the choir means to speak for or against something to people who already agree with one's opinions.

What is saying when an idealist, bookish inexperience, fresh-out-of-college employee/group of employees (like a department) is/are put on the helm (and given enough power) and they start to preach the experienced, practical, seasoned employee/group of employees (the other department) about te following:

1.) the ideal procedures and protocols that should be followed like obsession with standardization (even if these procedures are redundant to subject matters) 2.) Bring in ideas that are new and fresh for inexperienced but the organization (experienced Departments) have been tested and failed before. 3.) Bring in Over the top ideas that are simply laughable if exchanged in business circles but are given serious time of the day.

when they themselves lack experience of how the market, the industry or the world works.

Note: If you are thinking how could this be happening, this might occur in combination of nepotism, cronyism and/or in Laissez-faire or seagull management style

These inexperienced department who have power over the others departments but have zero experience with the other department's work flow, still just because they have been given power they preach the more wiser departments.

Answer 1

One classic idiom/proverbial phrase is "teach [one's] grandmother to suck eggs." Here is the entry for that phrase in Longman Dictionary of English Idioms (1979):

teach one's grandmother to suck eggs coll[oquial] to try to teach, inform, or give advice to someone who is more knowledgeable or experienced than oneself: he is always telling the director how to run the business; that's like teaching his grandmother to suck eggs {V[erb phrase]: often in Neg[ative] commands or advice, as in don't try to teach your grandmother to suck eggs}

Cambridge International Dictionary of Idioms (1998) reports that the idiom is primarily British and Australian:

teach your grandmother to suck eggs British & Australian to give advice to someone about a subject that they already know more about than you | You're teaching your grandmother to suck eggs, Ted. I've been playing this game since before you were born!

And the entry in John Ayto, Oxford Dictionary of English Idioms, third edition (2009) includes a brief note on the history of the expression:

teach your grandmother to suck eggs presume to advise a more experienced person. | The proverb you can't teach your grandmother to suck eggs has been used since the early 18th century as a caution against any attempt by the ignorant or inexperienced to instruct someone wiser or more knowledgeable.

One fairly early published occurrence of the expression appears in Simon Wagstaff [Jonathan Swift], A Complete Collection of Genteel and Ingenious Conversation, According to the Most Polite Mode and Method Now Used at Court, and in the Best Companies of England (1738):

Miss. Lord! I have torn my petticoat with your odious romping : my rents are coming in ; I'm afraid I shall fall into the ragman's hands.

Neverout. I'll mend it, Miss.

Miss. You mend it! go, teach your grannam to suck eggs.

And from Henry Fielding, The History of Tom Jones, a Foundling (1749):

'I should not have mentioned it now,' cries Partridge, 'if it had appeared so to me ; for I'm sure I scorn any wickedness as much as another ; but perhaps you know better ; and yet I might have imagined that I should not have lived so long, without being able to distinguish between fas & nefas ; but it seems we are all to live and learn. I remember my old schoolmaster, who was a prodigious great scholar, used often to say, Polly matete cry town is my daskalon ; the English of which he told us was, that a child may sometimes teach his grandmother to suck eggs. I have lived to a fine purpose truly, if I am to be taught my grammar at this time of day. ...'

Thomas Fuller, Gnomologia: Adagies and Proverbs; Wise Sentences and Witty Sayings (1732) includes "Teach your Grannum to suck Eggs" (as well as the closely related "Teach your Grannum to spin") but doesn't offer any further discussion of it. Forty years before Fuller, John Hawkins, The English School-master Compleated (1692) has an entry for "Teach your Grandam to suck Eggs." in a list of "English Proverbs Alphabetically placed." So the expression had already achieved the status of a proverb in the late seventeenth century.

Answer 2

I’ve heard this called “book smarts,” which implies a lack of practical experience. A more humorous description is, “well-read virgin.” More negatively, “smart ass” or “smart aleck.” I haven’t heard it in general use, but there’s a classic turn of phrase from an ancient Hindu scripture that’s stuck with me as a good description of this, of a student who “came back, full of knowledge,” and did this.

Answer 3

It was amateur hour.

amateur hour

(chiefly US, idiomatic) A situation or activity in which the participants show a lack of skill, sound judgment, or professionalism. yourDictionary.com

US
(On radio, television, etc.) a time slot in which amateur entertainers are invited to perform; (also in extended use) a period characterized by a lack of professionalism; an example of amateurishness or ineptitude. Lexico

The reference to amateurs doesn't mean that the newcomers necessarily lack training or education in their field, but rather lack experience, preparation, planning, etc., as if they were amateurs.

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His campaign lawyers were throwing spaghetti against the wall in hopes some might stick. It was amateur hour. C. Leonnig and P. Rucker; I Alone Can Fix It

He had wondered what kind of army sent loose ammo to outnumbered infantrymen whose lives were hanging in the balance. It was amateur hour, he thought. David Halberstam; The Coldest Winter

He started out with 150 cosponsors; I started out with zero. We were nobody from nowhere. It was amateur hour. We were doing everything for the first time and just going by the seat of our pants." Linda Killian; The Freshmen

"It’s amateur hour in Ottawa as the Heritage Minister seeks to salvage the botched broadcasting bill" Konrad Yakabuski; opinion piece in The Globe and Mail