LET ME BE CLEAR ABOUT THIS

"Where the law is uncertain there is no law."

Proverb

This applies equally well to rules, requests, orders, instructions, and all other forms of communication managers use with employees.

If it's not specific it doesn't exist, and when that happens, it's the manager's, not the employee's, fault. 

Knowing Who Does, Versus Who Doesn't

"Never offer to teach a fish to swim."

Proverb

Absolutely!

But when it comes to business how do we know who is and is not a fish?

Management: Put It In Writing?

"A verbal contract isn't worth the paper it's written on."

Samuel Goldwyn

What else do we need in writing besides critical elements of a contract?

Arguably a manager's instructions to a subordinate could (or should) easily include as much detail as would be found in any buy/sell agreement, but no one I know puts as much detail into their management directives as they would in a contract.

Is the fact that they don't the reason things often don't get done as the manager expects?

At what point should a manager's instructions be documented in writing? How much detail is needed?

Or is verbal direction between a manager and their subordinates always enough?