You paid a great opportunity cost. You could have been using something good for a year, rather than something designed to prey on your mind.

Every time you made a mistake, you lost a heart. Every time you lost your hearts, you were forced to watch an ad. That's great for Duolingo. You, on the other hand, spent a year being punished for making mistakes, which is the worst pathway one can possibly set up in a language learners' mind. I'm sure you can click on the words for 'Is the elephant under the chair?' very competently in the app now, but I'd be curious to see whether you've been Pavlovian-conditioned to fear making mistakes, and the impact that may have on your productive capacity in spontaneous language interaction contexts.

But hey, your brain is fungible, and VCs gotta get paid. That $14 billion valuation comes from somewhere.