Sometimes the rubber can break due to too much force....
Also cannot be 99.9% safe. That 1% (maybe one free-willy sperm) escapes and enters the egg....how then ? That's how some cases of shot-gun marriages happen.
safe condom usage is about proper procedure... if u dun know who to use it, its not so safe...
Read a story before... Back in India, there was a population control campaign and the govt officials went to distribute condoms to the villages... they had a hard time explaining to the villagers how to use the condoms, but in the end resorted to using bananas as an example...
One year later, the population was still exploding in the regions, so the govt officials when to check on what went wrong...
They saw condoms hanging on bananas on the banana tree...
Luckily they didnt use the bulls and cows to illustrate.
Else it would be really funny....
Haha... then the number of new calfs would reduce!