Do people not understand how birth control works?

Why do people freak out if let's say, you're on birth control and use it correctly and the condom breaks so he cums inside of you.

If you're taking your birth control correctly there's like a 99% chance it will work.

Theres nothing wrong with being extra cautious and using condoms ontop of BC, but why freak out? Like freak out enough to go buy a plan b? The plan b is the same thing as your birth control (well if you're on the pill or shot) but in a higher dose.

You're only supposed to take a plan b if you know you missed pills or took off your patch or something OR if you're not on any kind of birth control at all????

Google your birth control and how it works and how effective it is. If you're on pills, read the packet that comes with it. It tells you everything.