Here's the thing that makes Minecraft's world so much more dangerous: we have life-threatening creatures in the real world too, but they are living creatures bound to the laws of ecology; if you build a city without large herbivores, you can be sure that this city won't have tigers in it, because they need those to live. A tiger would need to physically walk from the forest to the city, with ample opportunity of getting spotted. Hell, killing the last tiger is a safe way to never have to worry about them again, since they need to reproduce sexually, and if there are no tigers left in an area then no new ones will appear out of nowhere.

Minecraft creatures, meanwhile, do appear out of nowhere. It doesn't matter if you've depleted the world of every last zombie, new ones can spawn absolutely anywhere, even within the safest possible area, all it takes is a small corner of mild darkness. Or does it? Because i've had random mobs spawn in extremely well-lit built environments where i was convinced they couldn't.

Minecraft's creatures cannot be definitively excluded from an area, nowhere is really safe beyond doubt even if the place is built entirely out of light-emitting blocks.

Then again, people do live in areas with venomous snakes and scorpions, those have a similar "potentially anywhere" threat as Minecraft mobs, yet people seem fine. They don't live in fear all the time. Then again again, snakes and scorpions are passive and only attack if you make physical contact with them, whereas Minecraft mobs actively look for you.

So yeah, nowhere is truly safe in Minecraft, there's genuinely always a possibility that you'll need to defend yourself from some horror.