[initplus]

This reasoning doesn't work because the market isn't a sequence of discrete binary choices. If the "opposite" of a bad strategy was a good one anyone could have great returns by designing some obviously terrible money losing strategy then doing the "opposite".

[hollerith]

Right, and even if the market was a sequence of discrete binary choices, bad traders will make many bad binary choices, but many of their choices will be good ones. (They just won't know which are bad and which are good.)

In other words, reversing every choice in a mediocre sequence of binary choices yields another mediocre sequence of choices.

[RhysU]

Taking into account trading costs, a meh strategy and its inverse can both lose money.