I think it's often misunderstood at how incredibly hard it is to stop reproduction.

For example birth control pills are 99% effective. From the NHS:

> When taken correctly, the pill is over 99% effective at preventing pregnancy. This means that fewer than 1 in 100 who use the combined pill as contraception will get pregnant in 1 year.

So, if you're in a relationship for 5 years, that's 1 in 20. For my group of people I know, this matches up pretty well.