You won’t be unprotected by missing a single pill, combined pills allow for 1 missed pill anywhere in the pack without it being a problem.
As for your question: your body needs at least 7+ pills in order to prevent ovulation from happening the following 7 days. So if you were to miss 2 (or more) pills and you failed to take at least 7 pills beforehand then that isn’t enough pills to keep ovulation at bay, making you unprotected. You can ovulate as soon as you become unprotected. That’s why.
