I totally missed it! In fact when my middie told me I was 10 cms I yelled at her 'why didn't anyone tell me I was in transition'
I think mostly I just didn't expect it to happen so quick, in hindsight I can remember the signs but at the time I wasn't expecting them only 2 hours in when I had been travelling fine until that point. I read lots of stories saying people just know when they are in transition and when to push but I just didn't, I totally didn't get the memo!