They like you to dilate 1cm an hour but that is absolutely not realistic especially given current birthing environments in hospital. I know my teacher Rhea likes to say it's active labour from 4cms and still early labour at 3cms, but no biggie in the scheme of things. Posterior like tiggy said can be more painful but it's not something you 'can't do'. Optimal fetal positioning can be helpful during pregnancy to avoid posterior presentation but of course doesn't guarantee anything, but it's believed to be of great help. It also doesn't mean you will be destined to have all posterior bubs, it's a positional thing and sometimes it can be because of the way things are physically - i.e. placenta position, pelvis shape - but it's not a guarantee either way.

I don't like the words 'failure to progress' because there is nothing wrong with the mothers effort or body. Something was going on (THAT WASN'T YOUR FAULT!), even fear can keep your cervix from dilating. If you had the whole fear, tension, pain, cycle going, unless you have someone really experienced in support to help bring you back it can be difficult to overcome. First births can be very frightening, we've never felt such intensity before and panic - they often do not go like we plan in hospital. Second births are usually much better. Your body has been in some labour before - it knows whats going on next time. You just need to focus on coping skills in labour with your support person, be it your partner, mother etc - HypnoBirthing is great. Being able to understand it at another level really does help. Having deeper understanding also brings with it more resolve if you need intervention. Because you know you needed it.