Unbreakable template
When looking at historical technology, I always use a template about prerequisites. I always assume that mechanical stuff was invented before electrical stuff, and more complex electrical stuff came after simpler electrical stuff.
This assumption is almost always wrong, but I never surrender it!
Nice example:
A military portable radio set from WW1. My template is puzzled! Why does the generator have a V-shaped padded thing between its parts? How does that fit on a car or truck?
Oh. It fits on a horse.