If you don’t name change it’s not actually that difficult.
Say you tell a story about eg a fight with your MIL at the school gate and then later wrote about it on MN. One of the school gate Mums might think “ooh, that sounds like Jenny”.
So she advance searches your username and discovers a thread from 3 years ago that mentions which part of the country you live in.
And another thread mentions you have a particular type of car because there’s enough room for three child seats across the backseat.
And another thread mentions your DH is an obsessive golfer and just spent £££ on xyz equipment.
And another thread mentions that you handmade your wedding dress etc.
Individually none of these bit of info are outing, but all together they can reasonably confirm the initial suspicion. Because the school gate Mum knows that Jenny who had the exact same fight with her MiL, lives in Cambridge with her 3 small children and her golf obsessed, BMW driving husband and dressmakes as a hobby.
It might not be enough to prove it in a court of law but it’s enough for reasonable doubt.
Probably every time we post we give little bits of info about ourselves. It’s not the individual bits that give you away - it’s the accumulation.
Which is why name changing is a good idea, and you should never post anything online that you can’t stand up to in real life.
And yes, I’ve recognised a friend, and no, her story wasn’t entirely comprehensive. People mostly post for validation, critical info is often missed.