This is not a very good analogy.

* You are one individual that averages 6 trades in month . GS has hundreds of traders, many of which do average that amount in a week (if not a day). The law of averages applies to GS, while your experience is anecdotal evidence.

In fact, if after 3 years with an average of 6 monthly trades you haven't liquidated a single negative position I'd say that most probably are making a classic investment mistake - holding onto your losses too long.

* GS trades much more volatile investments than you - futures, derivatives, etc. Traders have a much shorter time-horizon than you as well. You sell when you need the money while they're trying to meet their quarterly numbers.