Many analysts automatically assume that the underlying distribution of life data is Weibull. However, the resulting Weibull probability plot should be reviewed to determine if this assumption is accurate. If the plotted data points fall along a straight line, the life data actually does come from a Weibull distribution. If, however, the plotted data points do not fall along a straight line, the bad fit may be related to either the physics of the failure, the quantity or quality of the data, or the selection of an inappropriate distribution.