If they wait a while, the boy may become calm and more comfortable. (not just yet though.) At that time, he may be able to fly. At this time he is nervous as a person in a plane. That would be made worse if he flew it. Not just yet = not now but maybe later Just is added to other things dealing with time Just now = only a moment ago, seconds ago If you look at it in some other phrases, you will see a pattern... Just kidding = kidding, do not take this as a beg deal just a minute = not long from now just decide = do not make a big deal out of it, pick something just a dollar = it is not much money You can see that all the time it is used, just means "a little' or 'not much of an issue."

Just yet means it will happen but not right now. I will be making some modifications to my car, but not just yet, I need to have the money first.

The meaning is the same as "don't let him take over the controls yet." The "just" is used as a way to put more emphasis on "yet." It's a very bad idea (not just a bad idea) to let him take over the controls, because he's a nervous passenger and the consequences would be terrible.

The phrase "just yet" is close to meaning "at this moment" but "just yet" has a feeling of nervousness or hesitancy to it, as if someone feels unsure. It means that the timing is not right but perhaps will be better after waiting a bit.

In this context "just" doesn't mean anything. "Just yet" is more or less the same as "yet". "Just yet" implies a slightly shorter wait time than "yet". ^^ Hope this helps. :)