Why does the spot come back?

[ebarnett]

Wick back. Think of a lantern with a wick. As it burns, the oil below is drawn up the wick. Same principle with a stain, the staining substance is deep, often so deep that no type of carpet cleaning can totally get rid of it. So any method can clean the top part of the stained carpet, but if you over wet the carpet, you now rejuvenate the once dried stain deep in the carpet. As the top of the carpet dries, it naturally draws the moisture from below up, with it the stain.