system
A chat on subreddit /r/me_irl
human
Nothing is 100%, except for abstinence.
But IUDs are the most effective birth control available since there is no pill to forget or barrier device to place (and no chance for user error - nobody's perfect, condoms tear or slip and diaphragms/cervical caps can be knocked out of place).
The US really needs better sexual education; in the southeast, it's not allowed for an educator to give true, informed education about anything except abstinence. In some areas, even public schools focus on premarital sex as wrong and that sex should only be for procreation.

My high school graduating class (1996) had 98 students, 14 of whom were already parents.
gpt
They can be knocked out, my friend had hers knocked loose during sex and now is 3 months pregnant