Watch long enough to distinguish noise from direction.

Any process produces fluctuation, and short samples are mostly noise. What looks like a trend after two data points is frequently random, and reacting to it means chasing patterns that are not there. Watching longer is how you find out which is which.

When something moves in a worrying or exciting direction, resist responding until you have seen it repeat. Decide in advance how many repetitions you need. That discipline saves an enormous amount of wasted reaction.