When people say that they can't speak it, but can understand it, they're not saying that they can understand it at the same level they speak it.
This comes down to fundamental differences in memory and cognition for our brains' ability to recall information, or to recognize it. Generally, recall is harder than recognition, and in Second Language Studies terminology, it's part of the difference of "Production" vs. "Comprehension".
When you produce language, you have to know all of the words that are coming out of your mouth, and recall the vocabulary and syntax that form your sentence. When you passively listen to and comprehend a language, you don't necessarily need to know 100% of the vocab and syntax of any given sentence, because as long as you catch most of it, you can probably infer the general meaning.
I get that. But I feel like the aspect of time is being completely ignored by everybody else. Isn't this essentially recalling with a lot of time vs recognition with very little time?
I've been told my experience is common for beginners, but I've been studying for a bit over a year now and it's a problem that still lurks with me.