The famous game Paul Morphy played at the Paris Opera in 1858: White developed quickly, castled, and attacked with sacrifices against Black, who was behind in development.
The lessons of this game: development is time, open files are roads for attack, and the king of the side behind in development is in danger. These principles still hold today.
And the end of the game: Morphy sacrificed the queen and mated with the rook. Do you recognise this mate from the patterns in Unit 5?