Why does this piece of cloth collapse if I enable 'cloth collision'? I want the one piece to simulate as cloth, but it doesn't work.

If I don't check the "cloth collision", it works correctly. But if I check it, the one piece collapses.

I already tried to change some values on simulation tab but it didn't work well.

So please tell me what should I do?
I'm using blender 2.79b on Mac OS Catalina.
A trick that solves this issue most of the time is increasing the scale. Blender dont like small sized items in simulations for some reason.
Dont forget to apply the scale!