The first question is: "Given that markets constantly change, how can traders develop the psychological flexibility needed to adapt their strategies without falling into emotional overreaction or hesitation?"
Brett's response: This is a great example of a situation where improvements in trading process can create improvements in our trading psychology. Basically, what active traders need is real time information that tells them that their market is changing. The professional traders I work with at hedge funds monitor real time price change, of course, but also real time market volume and volatility and real time correlations. Very often, shifts in volume/volatility and correlations precede shifts in trading direction. A simple example would be a stock that moves out of a range to the upside but then stalls on low volume. If this was a valid breakout, one might expect short-term participants to take advantage of the move, resulting in increased volume and volatility. One might also expect that, if the stock's upside breakout was valid, it would be accompanied by similar moves in other stocks in the same sector and perhaps by similar moves in the overall market. By monitoring this real time behavior, traders can become highly flexible in jumping aboard moves or fading them. Once the market changes are perceived and understood in a broader context, the trader can quickly adapt.
Recently, the market made an intraday high but many sectors (including small caps) lagged significantly. This was very helpful information in fading the strength. Practicing trading with small size while making these observations and adaptations provides the experience that leads to confidence. How the market moves is just as important as the moves it makes.