Quote from atticus:
It was 1990-91. The first rule was to assume that you're trading outrights. The second rule was to never add to a loser -- you never know when the band will break. The third rule was to reduce size during reporting periods. Equity stat-arb is far riskier than any other spread-switch trade. Commit to a full position with a tight-stop. The mean-reversion koolaid is tempting, which makes it seem logical to add to losers. It's the same logic which makes fading price/oscillators so tempting in the "science" of TA.