Imagine if you met someone who can't eat watermelon. Not that they're allergic or unable somehow, but they just haven't figured out how to do that. So you're like "what the hell do you mean? it works just like eating anything else, you open your mouth, sink your teeth in, take a bite and chew. If you can bite, chew and swallow, you should be able to eat a watermelon."
And they agree that yes, they do know how to eat, in theory. The problem is the watermelon. Surely, if they figured out where to start, they'd figure out how to do it, but they have no clue how to get started with it.
This goes back and forth. No, it's not an emotional issue, they're not afraid of the watermelon. They can eat any other fruit, other sweet things, and other watery things ("it's watery?" they ask you). Is it the colour? Do they have a problem eating things that are green on the outside and red on the inside?
"It's red on the inside?"
Wait, they've never seen the inside? At this point you have to ask them how, exactly, they eat the watermelon. So to demonstrate, they take a whole, round, uncut watermelon, and try to bite straight into it. Even if they could bite through the crust, there's no way to get human jaws around it.
"Oh, you're supposed to cut it first. You cut the crust open and only chew through the insides."
And they had no idea. All their life this person has had no idea how to eat a watermelon, despite of being told again and again and again that it's easy, it's ridiculous to struggle with something so simple, there's no way that someone just can't eat a watermelon, how can you even mange to be bad at something as fucking simple as eating watermelon.
If someone can't do something after being repeatedly told to "just do it", there might be some key component missing that one side has no idea about, and the other side assumed was so obvious it goes without mention.
