Sex with someone new for the first time ...

Woman almost always universally 'compare' your 'performance' against their previous partners without exception and you get 'rated' (in their mind) against them, so a guy always has to be mindful of that.

Us guys generally don't give a flying fuck about previous romantic partners as ex's are ex's for good reasons and any pleasure had with them has been outweighed by the shit that caused the break-up's so it's not relevant.

Interesting that women are eternal hypergamists even with sex.