English and German split off from the same branch of the language family a long time ago, and it shows: Haus is "house", Wasser is "water", trinken is "drink", kommen is "come". For an English speaker, a large share of basic German vocabulary is recognisable within a few tries, which makes the early word count on a German course feel deceptively easy to rack up. Deploying that vocabulary in an actual sentence is a different matter, for three reasons that have nothing to do with how many words you know.
Compound nouns keep outrunning any fixed list
German builds new nouns by joining existing ones directly together, with no space and no hyphen: Hand plus Schuh ("hand" plus "shoe") gives Handschuh, glove. Kühl plus Schrank ("cool" plus "cabinet") gives Kühlschrank, fridge. Finger plus Hut ("finger" plus "hat") gives Fingerhut, thimble. This is not a party trick reserved for the notoriously long examples that circulate as jokes — it is the ordinary way German makes new nouns, on the fly, in everyday text. Once you know the parts, the whole is often guessable. But a word list built from a fixed set of entries will always be one compound behind whatever you are actually reading, because the language keeps generating new ones that were never going to be on anyone's list.
Separable verbs move the meaning to the end
A verb like anrufen, "to call someone up", looks like one word in the dictionary and is not one word in a sentence. In a main clause, the prefix detaches and jumps to the very end: "Ich rufe dich morgen an" — "I call you tomorrow up" — where an, the piece that turns "ruf" from vague to specifically "call up", does not arrive until the last word. Knowing anrufen as a flashcard entry does not, by itself, prepare you to notice that a sentence ending in a stray an several words later is finishing the verb that started it.
Subordinate clauses push the whole verb to the end
It gets more disorienting in a subordinate clause introduced by words like weil ("because"), dass ("that") or wenn ("if, when"): here the entire conjugated verb, not just a separable prefix, moves to the end of the clause. "Ich weiß, dass er heute nach Berlin kommt" — "I know that he today to Berlin comes" — leaves the verb, the one word that tells you what is actually happening, until last. English speakers have to learn to hold the rest of the sentence in mind and wait for it, rather than expecting the verb early the way English almost always delivers it.
The false friends hiding inside the cognates
Because so much vocabulary looks familiar, German is unusually good at hiding traps inside words that seem safe. Bekommen looks like "become" and means "to get" or "to receive" — Ich bekomme einen Kaffee is "I'm getting a coffee", not a sentence about transformation. Gift means poison, not a present (that is Geschenk). Rat means advice, not the rodent (that is Ratte). Each of these sits close enough to its English lookalike to slip past you unnoticed, which makes it more dangerous than an unfamiliar word — an unfamiliar word at least announces that you do not know it.
Watch Your Language is good at the recognition half of this problem: putting a word in front of you often enough, on your iPhone Lock Screen and Apple Watch face, that bekommen stops looking like "become" the moment you see it. It will not catch a compound you meet on a menu or in a work email before you do, which is exactly why you can add your own words straight from a photo, your notes, or a spreadsheet, so the vocabulary you are actually running into ends up on the list too.
What this adds up to
None of this makes German vocabulary hard to learn. If anything, the shared history with English makes early recognition faster than with a more distant language. What it makes hard is turning recognised vocabulary into a spoken sentence in real time, because German asks you to track gender, hold a separable prefix or an entire verb until the end of the clause, and watch for meanings that quietly diverge from the English word they resemble. Building the word list is the easy part. The habits that let you use it under pressure are the part worth practising deliberately.
