I really like you anology of friction causing sweat but also burning calories. I run into this same issue when building educational applications. I tend to slice it into efficiency and effectiveness. When we speak with students they always lean towards interfaces and flows that are efficient (as do we). However, learning science values effectiveness driving towards learning outcomes. You’d be surprised how many times this is as odds. Here is where some critical decisions need to be made. If we decide to make student sweat, we should be making sure that they are burning colaries (learning). I’ve been planning to write an article on the topic soon.