Everything that can go wrong will go wrong. And that is what we will discuss. When you build a model, you or somebody else is going to spend months of work doing experiments based on that model. How unpleasant if a small model error would make all those months wasted. This is part of another section in the course.
Many structures are a little bit wrong here and there.
Be total crap. Look at the validation report for 2GN5. Later, 1CRN got further 'improved'. Also, compare the 1CRN validation report with the 1CBN validation report . Spend some time on this, and when you are really sure about the answer, look at the comparison of the two structures.