From what I have read from people's informed responses on this topic, the idea of things being 'built to last' has an actual basis in history for several reasons.

I do not understand where the 20th century comes into this picture. Which is where a lot of us nowadays get our social pre-conceptions from (assuming a few generations' influence).

It seems like by the early 20th century, mass-production was becoming a thing. How far back can we go until this claim is not true anymore?