Here’s the tweet that started it all with over one million replies. ‘Are you happy or are you the oldest sibling and also a girl?’ The phenomenon has also now garnered 7.8 million views on Tik Tok with psychologists coming out coining it 'Eldest Daughter Syndrome.' So what exactly is it? Lizzie as an eldest daughter and Kate as an eldest daughter (sorry Jess you’re a middle child so you’re automatically forgotten) eduKate us on what it all means.