Until about halfway into my teens, no one told me that periods were painful, or involved behavior altering hormone releases. I thought my sisters were becoming moody & rude for no reason. I was generally aware of the concept of periods, but not of the broader effects. I feel I might have been much more sympathetic had I known.
Well, it's a spectrum. I worked with a woman that was spending the whole time in our office laying on the floor during her period because how painful it was. But I'm also married with a woman that doesn't have any symptoms at all and when asked about she said the only annoyance was having tampons ready.