Separate real problems from normal variation.
Data points are plotted over time with three reference lines: the green mean centre line, and the red dashed UCL and LCL at plus and minus three standard deviations. Points inside the limits are normal variation. Red points are signals. Rule 1: any single point beyond the limits. Rule 2: eight consecutive points all above or all below the mean. Rule 3: six consecutive points all increasing or all decreasing. The simulator lets you adjust mean, sigma, inject a shift and toggle a spike — all signals update live.
Reacting to every data point as if it is significant. A metric that moves up one week and down the next is almost certainly normal variation — reacting to it wastes time and creates noise. The control chart tells you when to act and when not to. A point inside the limits with no pattern? Leave it alone. A point outside the limits, or a run of eight, or a trend of six? Stop and investigate.