So, imagine if us humans could travel through parallel universes.

Awesome, right?

yes, but then there are some problems

maybe we might go into a universe with monsters and aliens trying to attack us!

but worse of all, we might just stop existing as soon as we go into another universe

for example

a universe where nothing exists, as soon as you entered that dimension would you stop existing,? or be the first thing to exist there,? but then how does that parallel universe exist?

Another notable paradox about this is:

a parallel universe where there are no parallel universes! That parallel universe would exist so it can't exist, and you're from another universe so how would you exist,? and what would happen to that universe?

Paradox by Rubarbranger