How do people end up pregnant at their 6 week postpartum follow up?

Not trying to sound ignorant. I just had a baby almost 4 weeks ago and I’m terrified of having sex any time soon!! I have 2nd degree lacerations during birth and the thought of anything entering down there frightens me lol

For those that ended up pregnant during their follow up 6 weeks pp….how ????? Lol No shame I’m just curious, I know everyone heals differently.