I like the idea of the interaction as transaction. It’s a more specific (and elegant) expression of the pain vs value calculation.
I have a couple of other conceits I have found useful, especially when leading a cross-functional group through product design.
- “What problem are we trying to solve?” is a nice simple stake in the ground to get people back on track. Can be applied to the large problem being solved that justifies the existence of the product. Can also be applied to micro interactions the user encounters while using your product.
- “What anxieties might the user have at this point?” is a nice follow up to question 1. Also can be used anywhere the user is interacting with your product, or even before the user does. Anxieties being things like, “Did that work?”, “How do I know this is safe?”, “How will I do the thing they’re telling me I’ll be able to do?”, “How long will it take?” and on and on.
To me, understanding the user’s anxieties and attending to them appropriately is where your product succeeds or fails.