Yeah, @markfoster is totally right about the wetness being key. It's that sticky, in-between state that lets you control the paint instead of it controlling you. Too wet and it just slides off like soap, but get it right and you can lay down a clean edge or blend colors without it turning into a muddy mess. I learned that the hard way trying to fix a patch on my wall, ended up with a weird drip mark that never really dried right lol.