¶ Overview
The language-learning app Duolingo has been in my life for about 3 years. In those years, I have learned a lot of German and a little bit of French and Chinese. The app is so interesting and captivating that I have spent 1001 almost-consecutive days practising. However, it is time for me to take a break.
¶ The day streak
Achieving a 1001 day streak in any activity shows a lot of persistence. I am happy to have achieved this milestone myself, and in this way have proved that I am sufficiently persistent. 
I hope this experience will make me more persistent in other areas of my life as well.
I have unfortunately become a slave to the streak, as for the last few hundreds of days, I have practised on Duolingo, not to improve my language skills or to experience fun, but simply to keep the streak alive. This has had an undesired effect of draining all the joy from my interactions with this otherwise awesome app. It really shows what strong effect such gamification features, like the day streak have on our minds. Nonetheless, it was I who made decisions every day to keep pushing and increasing the day streak, so I genuinely hold no grudges or argue against using this app.
¶ Cheating (?) tips
I have discovered these tips through my interaction with the app, but haven't abused them in my path to achieve 1001 day streak. It would simply suck the fun out of the experience, and I would not have felt proud of my achievement.
These tips are applicable at the time of writing (in 2022), but may become obsolete in later updates.
¶ Farming points on Legendary mode
After achieving the last level on a lesson (normally 5), the additional legendary mode is unlocked. This mode allows you to complete the lesson challenge an additional couple of times, but with less than 3 mistakes. By the time you get to this skill level, you should be making no more mistakes anyhow. This mode gives you an extra 40 points (with Duolingo Plus), which is quite a lot, so it is worth taking the effort to complete it. There is another catch - not to exploit this option, you can complete the legendary mode only 3 times for each lesson.
However, I have found that if you make it to at least the half of the legendary mode challenge in a lesson and then fail or quit, you will receive a consolidation prize of half the points (20 points) and the attempt will not be counted. This way, you can attempt the legendary mode on a single lesson infinite times, as long as you quit only halfway into it and pocket those 20 points each time. If you work on a single lesson, you will become an expert in solving those tasks and will be able to accumulate points quite quickly.
Additional improvement can be made by using Bonus skills (purchasable in shop). These skills max out on level 1 and once finished, you can begin Legendary mode immediately. They also exclusively contain only text-building tasks, which makes solving them a breeze.
Just keep in mind never to finish the complete Legendary mode, otherwise you lock yourself out of attempting it again.
¶ Automatic solving
It is possible to fully automate solving the tasks in each lesson, and it is not even that hard. I have inspected the information being sent between user's device and Duolingo servers, and it turns out that each message contains the correct result as well. This is meant for the app to be able to compare the user's solution to the actual solution and determine if the user solved the task on hand.
A programmer can easily abuse this information and make a program that solves Duolingo tasks automatically. This can be an interesting easy-level challenge to potentially try in the future.
