Why a mistake lowers one word, not the lesson

A sentence is not one thing

Take a short sentence: the children were playing in the yard. In the language you are learning it might be five words, and to write it you have to get a plural right, a past tense that agrees with that plural, a reflexive particle in the right slot, a case ending after a preposition, and the little words in the right order. Five words, five or six rules, and each of them can fail on its own.

If you write the wrong ending on dvorište, the past tense was fine, the plural was fine, and the word order was fine. What failed is one thing: the locative after u. An app that marks the whole sentence wrong and sends it back has learned nothing about you. It will show you the same sentence again, you will write the same four correct parts again, and you may or may not fix the fifth.

What the check actually does

Every sentence in the course knows which rule every one of its words carries, and which form of which word it is. When you type a sentence, the check does not compare your text to a single right answer. It reads every word you wrote, matches it against every accepted way of saying the sentence, and finds the exact word that broke. Then it names the rule behind that word.

This is only possible because you typed the answer. A tap on a tile tells the app which tile you chose. A sentence tells it what you know: which forms came out right, which came out wrong, and which word did not come at all.

What happens to the one that failed

Every word, every form and every rule has a level from 1 to 10, and a miss halves the level of the item that missed. Not the sentence. Not the lesson. The one form and the one rule that broke. The four parts you got right keep their levels and drift off towards their next, later review. The one you got wrong comes back tomorrow.

This holds across lessons. The locative rule might have been taught weeks ago, in a lesson you finished with a perfect score. If it breaks today inside a sentence about something else, it is that old rule which drops and returns to your daily pile. The course does not care where a mistake came from, only what it was.

Inside the session, the sentence comes straight back until you write it correctly. That retry moves nothing; it is early, and early answers never change a level. It only makes sure you leave the session having produced the right form at least once.

Where a typo is not a mistake

A slipped letter in the middle of a word still counts as correct, and is flagged so you see it. Writing igrlaa for igrala is a slip of the fingers, not a gap in your knowledge, and treating it as a miss would halve a level for nothing.

A wrong ending is never forgiven, because the ending is where the grammar lives. Dvorište instead of dvorištu is exactly one letter off, and it is the whole rule. The check knows which letters carry meaning in this sentence and which do not, so it can be generous about the one and strict about the other.

When you are sure you knew it

Sometimes you will miss something you genuinely knew: you read the prompt too fast, you were thinking of another sentence, your thumb hit the wrong key twice. The level is about to halve over something that was not a gap in your knowledge, and the system has no way to know that. So you can tell it.

Finishing a step of a lesson earns you a feather. A feather spent at the moment of a miss shields that answer: every word and rule it touched keeps its level. The item still comes back soon, because the feather protects the level, not the schedule; you will prove it properly next time. And a step pays a feather once, ever. Repeating a finished step pays nothing, so feathers cannot be farmed, and each one is worth spending only where you are honestly sure.

Why this matters more than it sounds

The difference between "the sentence was wrong" and "the locative after u was wrong" is the difference between an app that makes you busy and one that makes you better. In the first, your review pile fills with sentences you mostly know, and the actual gap hides inside them. In the second, the pile is made of the exact forms and rules you still get wrong, and nothing else. It is shorter, it is harder, and it is the only part of the language you still have to learn.