Why are condoms only 99.9% effective?

The packages always say that condoms are only 99.9% effective, that last 0.01% is it from breakage?

I thought it was 97%.
Anyway, because yes, sometimes the condoms break, slip off, etc.
The only method that is 100% effective is abstinence.
=]

condoms are only 97% effective if used correctly, not 99%
the pill is 99% effective at preventing pregnancy if used correctly
the condom is only 97% effective
and no, not just breakage
there are things that affect how likely it is to break
keeping it in a wallet for a long time for example, or using 2 condoms at the same time all make the condom more prone to breaking
no contraception or birth control s 100% effective
so theres a 1% chance that it wont work
also how you use it affects its affectivness
most people dont use them correcty so they have a higher chance of getting pregnant
certain lubricants or things people use as lubricant can affect them as well
if you use them past there expirey date they also have a higher chance of not working

Another failure point during actual use (as opposed to correct use) is not putting it on at the right time.
The penis leaks pre-come when the guy is aroused, and pre-insertion snuggling can allow some of this leakage to be left at the lips of the vagina, which can (low %) be problematic. And of course there is the ...let me just put it in just for a minute... plea from over eager, clueless guys.

If you ever are in the situation of condom breaking or slipping off, if you take the morning after pill, your chances of conceiving will be reduced by 70-85% if the pill is taken within 72 hours. (And some authorities say it might help up to 120 hrs.) In the US it is called Plan B, but around the world there are other brands.

Take care of yourself, and
Good Luck!!

No it is because some stds are small enough to go right through condums that is why. And birth control is because some times your stomoch produces anty bodys (my mom got pregnant with my brother on birth control)