I've been studying French with Duolingo for quite some time now. And Duolingo is almost like Pavlov's Dogs effect for me. I sit down, open the lesson, my brain switches into French mode then je comprends tout à fait! Sadly to say this but once I'm away from this site I feel I'm clueless... So I decided to expand my territory by saying to myself 'Je veux étudier le français' or 'Je dois aller dormir' etc. Je crois que ça marche.
That's normal, I think. When reading a book in another language, you feel you understand everything. And as soon as you would have to try to explain the book in your own words in that language to someone else, you get stuck. It just takes time and practice.
But your idea is really good! thinking to yourself in the other language helps.
(I really like your profile pic, RhinoBug!)
I have the exact same issue. I go on Duo and French is so easy for me, I remember tons, then I leave Duo and can't say even the most basic of things! Though thinking stuff to yourself in French (throughout the day) is a really good idea! I started doing that a while ago (before my French learning lapsed again) an found it really helped, though I could never remember very much, but I was improving.
I had that experience before! I could totally relate.
I've told this story on Reddit, but I'm too lazy to find, copy and paste it here, so I'll retell it as best I can.
Near the end of March this year, the school had a 7-day weekend (a week off of school), called March break. We went to Viagra Falls and passed by Québec, and boy, this encounter made me realize how big Québec really is.
This happened when we were driving back from Ontario to Nova Scotia. Now, when these trips happen at night, I sleep through songs by Michæl Bolton and Santana that my dad puts on repeat. After all, almost every sign is in French. Some of the names are really long. Hèque, there's even a place named Saint-Louis-du-Ha! Ha!.
Anyway, we pull up to a McDonalds near the highway. Remember the fact that I don't know where we are; that will be important for later. So, I see a sign called "TOILETTE". I'm too sleepy to know that it's French, so I ignore it. My dad and I were walking up to the cashier, and I rehearse my line in English. "Good evening, we'd like to order three cones of ice-cream, please." We go up to the counter...
...and the cashier spoke French.
I was mortified. I was too shocked to remember what il/elle/on/ils/elles said, so I tried thinking up what I wanted to say. Now, that I'm conscious typing this out, despite being on the Friends unit of the French tree, I can say the line as, "Nous voulons trois cônes de crème-glace," but I was still doing things before the first checkpoint at the time.
So, I stand there and just quietly mumble, "Nous voulons. Nous voulons..." over and over again, while desperately trying to think of the words to the rest of my sentence.
About thirty seconds of thinking went by, (which felt like an eternity, especially being next to a line with lots of people who probably speak French), when I realize I had downloaded the offline French translation file for Google Translate the night before.
So I quickly do the "rational" thing to do at the time and quickly get my phone out of my pocket, which was deeply buried in my pocket, due to the number of sleeping positions I could come up with when sitting shotgun in a large car for more than 10 hours.
I quickly type out that phrase, and my god, I sound awful with a sleepy French accent. Think of it like trying to pronounce Danish words when you've just woken up, but knowing it's probably too hard to pronounce, so you just pretend to choke for a bit until you get it right.
Around two minutes have past, since the Francophone cashier asks us for our order. My dad asks, "Is he right?" Flustered, the cashier responds, "Yes."
I saltily walk away while my dad casually chats with (thankfully) bilingual police officers and hearing the number ninety-nine being called out in French, (it was probably the order number).
We get in the car, eat our ice creams and went on our way.
After the next fully conscious moment in an Airbnb with really tall snow. I'm just sitting there just
watching r/AskReddit videos on my phone while ignoring the TV, which wastes electricity being immersed in the French of the news channel that was playing on the TV while breakfast was being prepared. Including the Duolingo memes that would come out after we came back, I realized, "That was really cringey. If you don't want that to happen again, use Duolingo seriously."
That was in late-March. On May 1, 2019, I started my streak up again, (kinda like starting a vehicle when you want to start driving), and I'm at day 22, since it's May 22 right now.
...and that's how I experienced the "forgetfulness" effect, and how I took learning on Duolingo more seriously.
I tried writing down sentences that use the vocabulary words I've used in a session, and I've done a great job. Like, when I see that signature white and blue, (soon to be gray, if possible), all the words I've learned just starts flowing through my mind, but when I have to write about something in general, I just start forgetting words, like, it's like magic, or something.