ALaughAMinute really? it isn't all about the finish and I wouldn't want to put the pressure on myself or the man I'm with to give me an orgasm when I know my body extremely well; been giving myself an orgasm since '99 after all.
Its not a very helpful thing to say when women struggle to orgasm for many reasons inc abuse, medical conditions, shame about their own bodies, traumatic births, pregnancy fear (this is big one for me due to repeat miscarriages. Best sex was with a man who couldn't have kids because that fear wasn't there at all) some medications even impact a woman's ability to orgasm.
I enjoy sex. I just struggle to orgasm and the last thing I am going to do is put pressure on myself. I can orgasm alone sometimes in 5 mins sometimes it takes 45. Just like with a partner it can happen quickly and leave them stunned or take a while/never happen. That's just me and probably a large percentage of women will have similar experiences.
With a partner it takes longer to get into the whole rhythm, being comfortable with each other to really let go especially if you have any of the difficulties mentioned above or are even just nervous.
If you've been together for a number of years achieving orgasm every time would be easier, not guaranteed, than a new couple who are still learning about each other and what gets them off.