[sandworm101]

The easy answer to the hard concept is that the big bang is not the increase in size of a thing. It is an increase in dimensions, including time. Our notions of size, of dimension, might not exist outside the bubble. We would therefore never perceive an edge, but that doesn't mean that one does not exist nor that there may be a finite size.

[Baeocystin]

I explain it to folks as if one was trying to go further south than the south pole. There's nothing physically impeding you; it's simply that once on the pole, all directions are north.

[regularfry]

Even that's not especially easy, because you then need to deal with "if the dimensions themselves are changing, why aren't protons the size of planets?"