It seems like the SPY(+1.74%) is attempting another breakout at its previously failed all-time high attempt at $333.08. From a technical perspective, a stock on an uptrend tends to stay in an uptrend unless something significant happens to change its course.
During stock market uptrends, most stocks tend to increase in price. That doesn't mean that they don't behave independently of each other. For this reason, using stop-loss orders will help you minimize losses in case the unexpected happens. As we know by now, the unexpected always happens.