Right, the concern is true. However, when that happens, arbitrage opportunities arise elsewhere (based on that correlation). As a matter of fact, one can start

Right, the concern is true. However, when that happens, arbitrage opportunities arise elsewhere (based on that correlation). As a matter of fact, one can start "betting" on the correlation being high and the only way for the "opponent" to win is to dislodge that correlation. In the end: technical analysis is useless by definition.