Cost, difficult, destructive, or too many players. Math models are either static or dynamic. Analytical models have closed-form solutions. Thus, math and dynamic. Need to fit a tool to the problem.
Time skips over events.
Incoming parts, wait, paint, and then into another bin. Modeled as discrete shows oscillation around a trend, whereas a continuous model is a straight line, hybrid is joined between levels. For given inputs, behaviour is not fully determined. Stochastic isn't quite the same. Can also model with other methods.