I actually read it in one of the sticky's.

"There is a common and strange phenomena that occurs with chronic
users. You would expect a chronic user to have the longest detection time
and the smallest chance of passing. This is not always the case. A
chronic user with a high tolerance will eliminate drugs quicker than an
occasional user. Chronic users have tested negative after a week long
binge. Lipid tissue also makes a huge difference." -- The Drug Testing FAQ (v4.11)