Ok, I messed up that attempt, but it's alright, because some planning is definitely in order. But, I sort of want to set that idea aside. I think I need to figure out what the criteria are for a "successful" Threadless design.

1) People want to wear it (looks cool, says something cool)

That's basically it. I think I need to mostly consider more whether or it's something people would want to wear. And why. It doesn't just look cool, it satisfies some aesthetic interest. To the extent that T shirts are an expression of the person who wears them, what do people want to say about themselves/what aesthetic do they want to associate with? Ok, keep thinking...

Ah, criteria 2:

2) Looks cool, but takes it to another level, employs a clever twist.

Right.