I think people greatly under estimated animals of burden and the wheel. We can see that from cultures that didn't have the wheel like the Incas. Treating disease/medicine was really unrealized until the modern age, it was not as important to the ancients. I also think labor saving technology in 19th century was really unrealized. I don't think people realized how much less manual labor we would need within their own lifetimes. There are so many small things that had a huge impact like the mould-board plow that made farming in North America possible.