People think that rockets push on the air, and that without air there is nothing to push on.
This is a very common misconception I think: people with physics or other science backgrounds (like me) have spent a long time more-or-less unconsciously training ourselves not to think like this intuitively, to the extent where we may end up thinking that people who do think like this are somehow stupid. But that's wrong: the way things actually do work is not at all intuitively evident to humans I think, and it requires a lot of training to develop the right intuitions.
As an example consider Aristotle's physics: he thought, among other things that among the fundamendal laws of physics were things such as:
- heavier objects fall faster;
- the natural state of things is rest (everything will slow down to rest);
- things don't move unless you push them.
Well, these are just hopelessly wrong as basic laws of physics, of course and someone with a modern physics background is going to laugh at them. But Aristotle was not stupid, clearly: he just hadn't developed the right intuition, because the experiments he could do were limited by being able to do them only in very specific circumstances (and he may have had funny-by-modern-standards attitudes to experimental evidence as well: I'm not sure about that). Aristotle's intuitions about how physics works were, simply, wrong. But it's also wrong to sneer at him for this, because it turns out it takes a lot of time to develop intuitions which either are not wrong or are at least less wrong (can anyone really develop intuitions about how QM works for instance: I don't know, but famous physicists have claimed they can't). And once you have developed the less-wrong intuitions it's then hard to remember that these were things you had to learn, simply because they are now intuitions.