Funnily all of Duolingo's retention mechanisms (formemost streaks and leagues) have the exact opposite effect on me. I am only moderately encouraged by success and extremely discouraged by failure. That means keeping the streak up is stress for me and failing a streak leads to a big negative impact on my motivation for the failure and a positive reinforcement of not doing it because then the stress goes away and that is nice. They literally train my brain not to use their app.