Luck, positive mindset and a doula.
I am a petite 5ft3 with narrow hips and I pushed out a 9lb1oz baby naturally. It wasn't perfect, but it was a very positive experience overall, and especially compared with most people I know.
My labour was very quick and terrifyingly intense. I was fully dilated and having absolutely terrifying double peaking contractions within 4 hours of the very first signs of labour. Getting to hospital in that state, and getting through triage at hospital was brutally uncomfortable, and most of my pushing was done flat on my back on a bed as they fished me out of the pool because they wanted to do continuous monitoring. Not ideal. I was pushing for between 2 and 3 hours and was struggling for energy and motivation by the end. BUT, I went through the whole thing feeling pretty calm and confident that I would do it and that it was all ok, all under control and
I had two wobbles- one when I was in transition (as I realised later) and needed to get up and into the car to get to hospital. I remember insisting I couldn't do it and I didn't want to go. And near the end of pushing, when he kept moving back up the birth canal after every push, I remember saying 'is there not a way we can just get him out?'.
I keep saying that my experience of birth is a complete contradiction- at once the single most painful and terrifying and overwhelming experience of my whole life, but also totally doable.
Obviously I was fortunate to not need any intervention, but I also credit two things. While I was pregnant I read only one book, Ina May's Guide to Childbirth. It was so calming and reassuring, and the birth stories in it stayed with me and just gave me this mindset that what will be will be and childbirth is positive and doable. And then on the day my doula was there constantly reassuring me that everything that was happening was totally normal and good and that I was doing fine and would get through it. It meant I just surrendered completely and focused totally on the moment rather than letting my brain take over which I KNOW would have resulted in me overthinking, panicking and labour probably slowing down. The end result was I got through the whole thing with no pain relief whatsoever. 9 hours in total and it was over before I knew it although there were individual moments that seemed interminable at the time.
I also went to an antenatal yoga class run by another doula which involved a lot of talking and relating of real life birth stories. That also helped me to go into labour very calmly.