Been wondering this for a while - like you're asking a question or saying something and your mind goes blank after saying "the" or "a". In German I imagine you wouldn't know which article to use before you know what noun you're saying, so do they tend to simply not use an article before they know what noun they want? Basically "forgetting" which article to use as well as the noun? Hope that makes sense.
Very often you have a vague idea of what you want to say, and with this idea often comes some words that have similar meanings, but still are not exactly what you want to say. So you often use their genders to find an article. And when it's wrong, you just correct it when you've found the right word.
Hast du meinen Schlüsselbund gesehen?
Ja, der liegt auf dem (short break while thinking of: Kasten, Tisch, Schrank) auf der Kommode.
If it takes longer to find the right word, you also might get something like this:
Ja, der liegt auf dem ... na, wie heißt das? ... auf dem Dings* ... na? gibt's das? ... Ah! Der liegt auf der Kommode.
*Dings, Dingsbums, Dingenskirchen, Zeug, Zeugs, Sachen, etc. are words that are often used as placeholder for words that in the moment don't come up in your mind. They all just mean: "thing". (Btw: English "thing" and German "Ding" are twin-words. They mean the same and they derive from the same etymological root.)