I love Duolingo. It's a super fun, super easy way to learn languages. I've become almost fluent in Indonesian over the past few years. But I hate the hearts feature. If you make five errors, you're kicked out of the lesson. Sure, you COULD go back and review the same easy lessons you review every time you need a heart refill. Your other options are to pay money or wait five hours for a single heart. This is extremely discouraging. I'm barely making progress & I don't enjoy using the app anymore.