In an early chemistry class, the teacher was happy to observe that atoms bond in certain ways, with a certain number of slots available per atom (depending on element), presented various molecular diagrams, and mention that while some combinations don't seem to occur in nature, some have been created artificially.

Some kids asked about molecules they had just imagined. They were reminded that some molecules don't seem to exist, or told why what they were proposing didn't fit the model.

I asked somethnng like, "If the model's rules allow that atoms would be able bond in ways that are not observed, doesn't that mean that the model is incomplete or incorrect?".

The teacher was not pleased, and became dismissive: "The model is complete, and correct.".