So. Yeh.
You really have to drill home that ideas and possibilities are just that, and not concrete features that they could start using tomorrow.
I ask because this guy s a common lament, but I’ve never figured out why. It shouldn’t be a surprise or (to me) disappointment that the fidelity of a communication also carries signal about the status.
Example of this from another industry: working in manufacturing, a client wouldn't listen to our explanations about why their part wasn't ready to be molded in plastic. (lot's of design issues that would make it impossible to get out of the mold or lead to extreme cosmetic imperfections). To prove their point that their part designs were ready, they held up a 3d print of their part and said, "See? It's right here! You just have to do this!" This led to a half hour of answering questions before they started to understand that the two fabrication processes were very different and had different requirements.
I think the unfortunate part is really the time you have to sink into helping someone understand that's often unpaid, in my experience.
So we, unfortunately, have to make effort to dumb down, or at least carefully manage, the fidelity of that part.
Any change from that haphazard throwaway with nice colors is suddenly a change they have opinions about, because it feels like a change.
If you show them something that's obviously not what will ship, they don't get as attached.
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This is also partly a "most people don't understand the design process" thing, and just how much reworking and restarting is generally necessary to get an actually-good end result. If they see hundreds of mockups (or even sketches), they'll wonder why you haven't made hundreds of products, rather than those being merely tools used to think along the way.
Actually I don't think "technology producers" are entirely excluded from this bias either. I've assumed more complexity than there was in reality (possibly due to my background in infrastructure and backend), but other developers I've worked with certainly fall more into the trap of "there's a UI? now it's just a simple matter of CRUD."
Personally I also prefer the hand-drawn style, but can't put my finger on why. There's something about the uneven lines filling out the space better, while still defining the shapes well.
Lower fidelity puts the viewer in a more conceptual mode of assessment, and there they can more easily perceive the clearness/approachability of your concepts.
I think this was then expanded to be "paper-looking".
But yes, for the reasons you state.
If everything is either an obvious sketch, or pixel perfect you can get decent feedback, but a design that is just a little off in jarring ways will distract people from the functionality or design intention.