Or: Don't design a product that needs instructions on how to use

That's a high bar to set.

Kind of like saying "don't design a laptop uglier than a Macbook." Sure, you can do it, but you may be optimizing the wrong thing (and/or at the wrong time).

Maybe, but it's the bar for successful webapps nowadays. People are familiar with a set of functionality; if you change them, make sure it's intuitive or obvious.

Or: Tell me WHY to use the product. This is a much more common failing, IMO.