Originally Posted by
Quinnleigh 
Any doubting of the decision [to quit for good], even the tiniest hairline crack, and the beast slips through.
The doubting IS the Beast. Quickly listen to what it says (the AV), but do not answer or act upon it any more than possibly saying with deliberate calmness "F*#@ You!" Then back onto what YOU were thinking and doing.
The Beast cannot "slip through" anywhere without YOU very deliberately opening up that crack in full consciousness and watching it come through and then YOU listening to and obeying what IT says.