As much as men and women are meant to be together, both sexes consider some things as sacred which shouldn't be tampered with by the other sex.
Females are known to love their personal space. They don't take lightly men invading into their 'inner sanctuary' unless they are permitted to do so, doesn't matter how awesome their relationship is.
From small intimate items to small women talk, these things may mean little to the menfolk but it surely means a lot to these women.
1. Make-up: Your girlfriend/wife wants you to see her as pretty all the time. You don't have to worry your head about how she does it.
2. Sexual escapades: Unless you are her male best friend and not a boyfriend, this is simply a no-go area for you. Most women would rather share this detail with a female best friend.
3. How she feels about his family: A wife/girlfriend may not want to express herself over her man's family because she may be accused of being insensitive. Women try as much as possible not to cause a rift between her man and his family so she'd rather keep her opinions to herself.
4. Small girl-talk: Just as men have their guy-talk, women do there's a lot but in hidden areas. Don't expect your girlfriend to tell you her best friend's well-kept secret, as long it has nothing to do with your relationship.
5. Talk of her ex-boyfriend: She likes to save the detail for herself. Telling might just hurt you. But of your girlfriend decide to spill a little, know that she did it for a reason.