Whilst a lot of these ideas are now widely known to be not true by the majority of the public, they are fascinating to comprehend by today's standards, and are actually beliefs still held by some people!
A common line taken by people is the idea that Marriage used to really 'mean' something, often citing divorce statistics. However, the only reason that divorce figures were so low is not really due to some fortunate fact that everyone was beaming with joy all the time, but really the fact that divorce was so heavily stigmatized by society that most women would be subject to heavy personal backlash. Also, the process was far too expensive for most people and was therefore only a viable option for those who were wealthy.
While there's nothing quite like proper home-grown and cooked food, this claim isn't necessarily as straight forward as it seems. The idea that people ate 'proper food' back in the 20th Century and so were much healthier as a result is not necessarily the case as starvation rates were massively high throughout the early 20th century due to a lack of viable food and ultimately caused the deaths of millions upon millions over the course of the 20th century as a whole.
Okay, while there is a problem with doctors occasionally over-prescribing tablets such as antibiotics, the idea that my grandmother frequently used to tell me that 'people shouldn't be taking all this modern medicine' is a little hard to swallow (see what I did there) when the average life expectancy has risen from 31 (early 20th century), up to 79 by today's standards.
Yep, this is a weird one. It was a surprisingly common notion that women never used to suffer from oncological conditions due to the fact that they were frequently giving birth, a process which 'rejuvenates' the body. However, we now know that this is not true, most women who lived in the countryside simply weren't diagnosed with these conditions because healthcare was so poor there at that time.
Another idea that a lot of great-grandmothers held was the idea that women are fine to be back with their nose to the grindstone the day after giving birth. It was common practice in the early 20th century for mothers to be back at work after their maternity leave (which could be as short as a few days before giving birth) which meant that issues such as post-partum depression and physiological issues such as uterine prolapse caused from frequent childbirth were both ignored and common.