More forgotten knowledge:

In the matter of eggs, it's an old timing issue. People didn't have hot running water in those bygone days. The traditional timing of the perfect egg comes down from those days.

A long time ago…

When Mother told me, as a young girl, how to boil eggs, she said to put them on in cold water. I asked why and she said that's how her mom taught her. So, me being that kid with all the questions, I asked Gran. She said that how they'd always done it, that her mom taught her that way too. I turned to Gramma Mary to find out why.

Gramma Mary explained that you couldn't get hot water from the old pump. She said back then it was common to keep a big coffee pot of water near boiling on the back of the stove so as to always be ready to produce hospitable pot of coffee or tea. The reason you didn't use that was hot water for the eggs was because dropping a cold egg into near boiling water would crack the egg. And, timing the boil for the perfect egg was figured out for starting in cold water.