Good points in the article but my only problem is with this statement:
"It’s well known that users don’t read instructions, and they are particularly less likely to read instructions at the top of a form. Form fields seem self-sufficient — after all, each field has a specific instruction — its label, why would you need to read anything else to fill it in?"
Should we not question why users don't read instructions? I am not saying we should put instruction in place of something that does not need explanation but I am not sure if by acknowledging people don't read we are solving what the actual problem might be?
The word intuitive literally means: "insight, direct or immediate cognition, spiritual perception". One can accomplish something via their intuition and be right, just by looking at the form. The form should carry and convey all the information necessary — quicker to fill out. That is the spiritual reasoning for a web form to exist, after all — to collect information and be filled out.
A lot of this is interaction design 101 stuff related to friction and brain modalities. Not sure there's new ground to be discovered from deep diving in to the psychology. I certainly won't stop you from ruminating on it further, though.
NNG is targeted at design and product manager professionals that would likely already have extensive knowledge of these concepts.
I personally struggle with this when it comes to forms where 99% of the fields are required, and thus making the outlier (optional) the thing to flag. Seems the former might be excessively noisy, but I'm not sure.
I came across this approach a while ago: https://uxdesign.cc/form-field-required-vs-optional-9b4d7cdbf400
Their solution was to only mark the optional fields which I prefer because it naturally implies that unmarked fields are required and cuts down on repetitive details.
It is probably important to consider the ratio of required to optional choices, because if a good portion of your form is optional, the noise level goes way up and you have the same issue. But that scenario suggests there are some bigger problems at play with the form.
When it comes to consumer forms, like account registration etc., I personally feel that optional questions should not be included. If you want users information then actively seek out users and engage with them or send out surveys to get them to offer their details. Optional fields are lazy, bothersome, and often marketing related.
Thanks for the comment, very useful to consider!