Grammar is stored in your
procedural memory. That's a fancy way of
saying the stuff you do without
When you ride a bike,
that's procedural memory in
action. Swimming. Typing. Breathing. You get the idea.
When you learn by memorizing rules and filling in blanks, that's like trying to learn to ride a bicycle by reading the manual.
It just doesn't work.
Find the clues to understand for yourself. Then use it. In your own works.
When you're in the situation - just like riding a bike - speaking will happen without thinking. Your brain knows where to find what it needs.
Think of a book you read last year. What can you still tell me about it? The main character's name? Specific details or scenes? Or can you only summarize, what was the book really about? Not the plot necessarily, but the theme. Most people can do the latter if not a single detail. Why? Because getting the theme is understanding. When you come to your own understanding about something, memorization is all but irrelevant.
With the carrds, you figure out what's going on. No one tells you things, you've got to turn on your own brain.