You know the game-changer feature is on the 3rd sublevel of the hamburger menu because you've spent all sprint staring at it. Your users, less so.
Disproof
A documented flow in which each user type gets to the point where they can even begin to derive value from the product
Consequences
If you're making this kind of mistake, you likely didn't just forget to tell people how to use your product, but also forgot to tell them why to use your product (see messaging).
Nobody knows how to get value out of your product - which has the same consequences as not delivering value. Which means they don't use it and you lose cohorts worth of users which cost triple to re-aqcuire
You also multiply errors as you double down on functionality that you don’t realise is useless because nobody’s used it yet, thinking you just need to keep building until it's 'complete'
Causes
Sometimes, a product that’s supposed to ‘self-teach’ via UI/UX ends up with the UI/UX dropped from the build to speed time to market
Or the " we don’t need onboarding, we're talking to the users already every day" model that blows up the moment you scale past 5 customers. Unfortunately early success tends to blind you.
In B2B products, tends to happen when the sales team flies solo because having anyone else (like, god forbid the people responsible for customer success or building the product) around would ‘slow things down’
Approaches
It doesn’t matter if you use an onboarding team or in-product tutorialisation. If you haven’t got a map of every learning step the user takes to understand how to get value of the the product, start there
Any plan, be it via UX or AM, is useless if you haven’t sat down with actual users and built the plan around where they actually get stuck. Otherwise you’re both guessing at the value of the product and at how to get the user to that point