The pill and what makes it less effective!

So this isn't really a question . It's just Alittle bit of information for all you women on birth control. But I'm was watching a closer look teen mom from Tuesday night . And I just learnt that if you are on birth control and you have diarrhea it makes the pill less effective. How come I was never told this when I started the pill? Thank goodness I switched to nuvaring when I was younger .