I just don't get it

"Through thick and thin."

Right. So I get the gist of it - like, if someone, say, Wentworth Miller, were to look down into my eyes and whisper tenderly 'Jacki, I love you more than anything. I'll stick with you - through thick or thin', I would get it.
Through good times and bad times, right?
Right.
But...which is thick, and which is thin?
WAIT!
Because I know what you're all thinking: Thin is bad, thick is good. Dumbass.
Yeah, well that's what I thought too.
At first.
I mean, that could be right - during bad times, there isn't much good stuff, right? So, if you were to squish all the good stuff together into a human shaped...thing, well, it would be a thin human shaped thing, because there wouldn't be much good stuff to squish together!
Oh, I don't know why its a human shaped thing. Just go with me on this.
So yeah, that's why that makes sense.

BUT.

What about if thick means bad?
I mean, that could also be right - during bad times, there's lots of bad stuff, right? So, if you were to squish all the bad stuff together into a cloud shaped...thing, well, it would be a thick could shaped thing, because there would be heaps of bad stuff to squish together!
Also, bad times are hard, right? And thick things are also hard...like, hard to walk through. Have you ever tried to walk through a swimming pool filled with maple syrup? It's hard!

Alright, now I don't know what confuses me more; the saying "through thick and thin", or how I ended up talking about trying to walk through a swimming pool filled with maple syrup.
Well, I don't really know which is which - all I know for certain is that I... am an idiot.