Why are condoms not completely efficient, even with perfect use?

Question

My doctor told me that 1 in 5 women using only condoms will get pregnant per year of use... I don't know if that's necessarily true but, I know condoms are not completely efficient, even when used perfectly.

Why aren't they completely efficient, if you use them perfectly, and there are no leaks and no breakage?

Answer 1

You should use pills as well.

Hey I think I'm the only guy on this section.  

Answer 2

accidents happen they break and etc

Answer 3

Condoms are for noobs... just don't have s*x and be a virgin. Problem solved.

Answer 4

A condom failure rate of 1 in 5 is not from perfect use but rather typical use.

Perfect use of condoms has approximately a 3 in 100 failure rate.

I guess the failures are due to things like manufacturing errors and use of expired condoms.