An engaging teacher makes the effort worth it. So it doesn't feel like the contrast effort required if oriented horribly. I fully believe there are good teachers and bad teachers. But that's why I used the word biology: there is no way to learn without effort. Your relationship with the effort is the important point.

> Duolingo is just one example that there is plenty of money to be had even with dubious claims and a product that doesn't actually work that well.

That's my point, it doesn't actually work for learning. Duolingo sells feel-good vibes of being productive with your doomscrolling time. It's learning-porn basically (could be worse).