There are two popular language learning software platforms: Anki and Duolingo. Anki is hard, free and effective. Duolingo is easy, commercial and ineffective.
The number of Duolingo users far outstrips the number of Anki users. Duolingo has 8 million downloads on the Play Store. Anki has 40 thousand. So there are 200 Duolingo users for every Anki user. If you ask a random language learner what software to use they will probably suggest Duolingo. If you ask a random successful language learner what software to use ze will probably suggest Anki. Most language learners are unsuccessful.
It should be no surprise that most language learners use an ineffective product. Learning a language is hard. Duolingo is designed to attract as many customers as it can. Therefore Duolingo must be easy to use. Anki is designed to work. Therefore Anki must be hard to use. Effectiveness and mass-adoption are mutually exclusive.
On average, you will have to ask 200 language learners what software they use before one of them tells you about Anki. In practice, you are unlikely to stumble across Anki at all. You can only find out about Anki if you go looking for it and you will only go looking for it if you already know it exists.
No one ever told me about most of the software I use. Usually I will infer that it must exist and then go looking for it. This is how I discovered qutebrowser, Spacemacs, tmux, i3 and—of course—Anki.
This principle is not limited to open source software. Everything I have ever taken seriously exhibits a similar pattern. There is a common way most people do it and there is a cheaper, better, skill-intensive way a tiny minority do it.
Minority opinions are inherently controversial. Here are a few relatively uncontroversal examples to illustrate the trend:
|turing-incomplete hotkeys||Vim keybindings|
|programming languages without syntactic macros||Lisps|
|the desktop metaphor||tiling window managers|
I do not mind choosing to be part of the majority. I watch mainstream movies. I eat at popular restaurants. I perform the oldest magic tricks in the book. I am okay with these choices I know about.
I make most of my choices unknowingly, by default, from the options presented to me. Most of the time I pick Duolingo over Anki without ever knowing I have made a choice.
 I am ignoring the Anki desktop app, the med student userbase, the paywalling of the iPhone Anki app and differences in churn to simplify this example and because I do not have the relevant numbers. ↩
 I mean that effective spaced repetition is inherently difficult. The Anki onboarding experience could be improved without loss of utility. ↩