Agnieska Murdoch warn’s about The Dark Side of Language Learning.

While learning a language can be an exciting adventure, it’s not just a question of putting in the time and maintaining motivation. You will encounter actual stumbling blocks and a critical language learning skill is dealing with frustration. A lot of language learning programs aren’t very direct about this, which is unfortunate because it can leave the learner feeling that they’re doing something wrong. This is why it’s useful to read the experiences and advice of veteran learners, not just the book jacket or promo blurb for language learning programs.

There’s also a pretty nice take on this in Viktor Dessov’s Everyone Can Learn a Language Efficiently:

[L]earning a new language is not a straight-forward process of getting more and more confidence in one’s speaking abilities. It has its uphills and downhills. On several occasions you may feel quite unhappy with having initiated this endeavour in the first place.

Dessov, Viktor. Everyone Can Learn Languages Efficiently: A Comprehensive Guide to Becoming a Polyglot (Kindle Locations 75-77). Kindle Edition.

In this passage, Viktor goes on to explain some of the highs and lows you’ll encounter, like moving from triumph at your first real sentences to frustration that you sound like a caveman, and from being able to chat about everything to realizing you’re hopelessly outmatched if you want to argue a point with a native speaker.

We should be more honest about the ups and downs of language learning, though it’s true that most of the Learn Fast with No Effort books and programs only carry you to the first high of making your own sentences. If you’re learning a language for any reason other than because it’s what those around you speak and you won’t survive if you don’t learn, be aware these frustrations are coming and have strategies prepared like switching between programs or taking a break to consolidate with listening because you won’t have a lot of extrinsic motivation to learn.