Clothing system doesn't work

According to this video tutorial from YouTube: UE4 Tutorial: Cloth Simulation (See description) - YouTube

I come accross every step of it, but when I apply and paint on the designate object. After active, it seems my object’s area that I paint on doesn’t affect along gravity. It is still settling in the same post all the time even I drag it in the scene. I wonder that do I need to enable anything in term of activation?