The following is an example of human stupidity, because natural, cheap, and fairly safe methods of birth control are not taught and fairly unknown.

Now there is a NATURAL method that is very safe. Even more, if you use only 1) 2) and 3), even the catholic church allows it and if you do it right it is pretty safe.

1. the calendar method gives you a basic idea of your cycle. Pretty bad method if you do it alone, unless if your cycle is extremely regular. Need to study it to do it right, most people do it wrong.
2. the cervical mucus method is extemely safe when practiced well (but requires some intelligence)
3. the basal temperature method as additional third method further increases the safety of these methods
4. By these methods, at least 1) and 2), or maybe all 1) and 2) and 3) you can know quite precisely
   1. on which days you are very fertile (actually this method is used by doctors to get women pregnant on purpose),
   2. when you might be fertile
   3. when you can be pretty sure to be infertile
5. for the paranoid, the safety can be increased greatly by using another method, like condom and withdrawal, the following way:
   1. when you are infertile, have sex with condom (very safe, double security)
   2. when you are fertile or potentially fertile,
      1. dont have any sex at all (obviously very safe)
      2. have sex with condom but the man withdraws before orgasm (double safety: condom and still no orgasm inside the woman)

Basically, this is fail safe by using double safety, like in Engineering

Also, it is important to use condoms correctly:

1. Buy good condoms
2. store them correctly
3. use common sense: use (appropriate water soluble) lubricant if there is not much lubrication, feel when the condom is likely to break or come off because of too much lubrication inside
4. immediately stop after the man’s orgasm. A condom full of sperm can slip off or sperm come out at the base.
5. Withdraw the penis while holding the condom

http://en.wikipedia.org/wiki/Billings_ovulation_method