Pill - difference between missing a tablet and having a 4 day break

[Lifeisupanddown]

This question has been in my head today. If I miss a pill or two, I have have to use extra contraception as there is a pregnancy risk. But when i have my 7 days pill free days then I'm covered?
I can't work this logic out, can anyone explain?

The pill regulates your menstrual cycle. If you miss a pill mid cycle you might ovulate. The break is when you bleed (menstruate) and shed the lining of your womb, so is a different part of your cycle.

If you have taken 21 pills then you're covered against pregnancy in your pill free 4 days/week. If you've taken fewer than 21 pills when you miss a pill then you arent covered against pregnancy. You need at least 21 tablets so the hormones build up to cover the days you don't take them

You have to have been taking it for at least 3 weeks before the break, then you'll have a withdrawal bleed and won't have ovulated.
Missing at pill at some points in the packet will mean you could ovulate and get pregnant.