When talking about languages, people sometimes say language A understands language B but language B doesn’t understand language A. How can that be?

Question

The way I see it, if one understands another language, it’s because of similarities in syntax, grammar, etymology or what not. But a similarity is by definition bidirectional, is it not? Is the idea that some languages understand other better than they are themselves understood a lie?

In: Other

Answer 1

For example you can have a grammar structur that is very basic in one language but complex in the other but they share the same basic rules. So the side with the complex grammar understands the one with the basic grammar but the side with basic grammar doesnt understand the more complex grammar. They will still understand some things but it will be much harder.
Like you have two languages that both use the same word order. But when talking about the past the more complex one changes the word order while the basic one just adds a word that says this happend in the past. You might not say a sentence in that way in the language with diffrent word order but when they will understand otherway around they wont understand unless they know that this diffrent word order means it happend in the past.