I figure its ...error margin? ie. slippage, breakage, coming off, using mosturiser on your leg/face/hands ..etc etc
sure someone wise will come along shortly..lol
was trying to explain to my oh that they arent reliable... he was like "huh"..i never knew that.. :-o
i would say your right. some things make the condom basicly brake like lipstick, baby oil and many other things i believe i was told cheesse also has the same effect
also the things of putting it on with an air pocket it side it likely to make it blow up when he blows so to speak. as well as some lubes are not ment to be used with condoms so you should always check the bottle/tub ect
oh also the friction from the man bits and women bits can make the condom brake if your no erm wet enough
EDIT:
just found this on website to give more info
1. The condom is past its prime. Condom wrappers have an expiration date on them, so be sure to take note.
2. Storage issues. Heat damages latex condoms, so they shouldn't be kept in a hot place such as a glove compartment or a wallet. Keep them in your medicine cabinet or nightstand instead.
3. Lack of lubrication. If there is friction while having sex, especially anal sex, not only will it cause pain and irritation to your privates, but the condom can break. So be sure to use lubricated condoms or use extra lube if you need to.
To hear the other three reasons read more.
4. You're using the wrong lubricant. If you're using latex condoms, oil-based lubricants can weaken the rubber and cause a tear, so use only water-based lubes.
5. The condom doesn't fit. If the condom is too small or too large, it can rip, so experiment with different sized condoms to get a snug fit — not too tight and not too loose.
6. The woman is tight. Some women's vaginal muscles are naturally tight, so to help prevent condom breakage, lubrication (and a lot of it) is a must.