@Leif Goodwin
You may be right when it comes to books that deal with language learning in theory. To be honest, I haven’t read much of that kind of stuff. The only app I use is LingQ. And I don’t use it to learn languages (in my opinion, LingQ isn’t suitable for that), but to expand my vocabulary in languages I already know quite well and to train my listening comprehension. So I was mainly referring to language courses with textbooks and CDs, mp3s, etc. I don’t know what it’s like where you come from, but here in the German-speaking world, authors of language textbooks usually recommend regularity without interruptions. If it’s different where you come from: Lucky you.